It is four decades now since Joni Mitchell was designated DeMolay Sweetheart, poster girl for the youth offshoot of a masonic organisation in her Albertan home town. Hands rising to form an imaginary cone above her head she depicts her 16-year-old self sitting beneath a dryer within the pretend salon used to train those would-be hairdressers among the student body. And while awaiting the unveiling of the kind of big, twisty beehive befitting her soon-to-be-confirmed status, she frets about an assignment she has to carry out for a creative writing class. It is a poem on any subject, and in blank verse.

"So, awaiting inspiration, I pick up this copy of a movie magazine, Silver Screen..." Within it is an article on the reigning youth idols of the day, recently weds Bobby Darin and Sandra Dee. "And it's this really terrible piece, exposing their marital distress. I feel so sorry for them, but, well, suddenly I have my subject matter. I write my poem straight away!"

Mitchell says she hasn't so much as thought of it in an age, but still is able to dredge up from memory this piece of ancient coursework."The fish bowl is a world reversed," she recites carefully, "where fishermen with hooks that dangle from the bottom up/Reel down their catch without a fight on gilded bait/Pike, pickerel, bass... the common fish ogle through distorting glass/See only glitter, glamour, gaiety/ Fog up the bowl with lusty breath/Lunge toward the bait and miss/And weep for fortunes lost/Envy the goldfish? Why? His bubbles breaking round the rim/While silly fishes faint for him and say/'Oh my God! I think he winked at me!"

Today, it is the irony contained within those teenage lines - and the preternatural insight into a celebrityhood she says she never sought - that amuses her. "It's like the gods - or God, whatever - said, 'Yep, she's got a pretty good inkling of it. But let's have her experience it first-hand all the same!"'

When she smiles or laughs, which is often, the face of the most accomplished, most extravagantly gifted woman writer-performer of the rock era lights up from within, appears as hopeful and free of guile as it must have been those 40 years ago. But, Mitchell (still smilingly) insists,"I'm an old babe now. I'm easy to kiss off. I'm of an age when husbands run away with younger models. In the whole sex exploitation-ness of it all, I'm o-l-d.."

Hardly. She is 56. Which, and here's her point, means near-Jurassic according to the orthodoxy of the record industry. In capsule form, this is her career within it. Lauded, loved, elected an icon of the era while in her twenties. Slapped in the face with the critical backlash - this despite delivering peerless, unlikely-ever-to-be-bettered work - in her thirties. Sidelined, largely overlooked, in her forties. Then, finally, re-appraised, invited back in from the critical cold by a rather redfaced taste-making elite on entering her fifties. For in recent years, praise, citations, trophies have rained down on her like confetti upon a bride.

Is she grateful? Actually, not very. "When you're truly honoured, it's humbling," she allows. "But, when you're insincerely honoured, it makes you - makes me - arrogant. The last thing I want to do is go to these award ceremonies and appear cocky but, unfortunately, that tends to have been my response in a lot of cases. It brings out the wrong side in me.

"Someone coming up to me on the street and saying that they love what I do? That kind of reaction is not coming out of a sense of appropriateness. That is coming out of kindredness. Which is wonderful, if embarrassing for both parties. We're strangers, after all, and a lot of times those people are so earnest and overwhelmed that they look as if they're going to implode. The only possible response is to give them a good hug, which I do. And that makes for a very real and sweet encounter. Those people whom I've hugged on the street - they're the honours and the good reviews." Was there no pleasure to be taken, then, in the double whammy of Grammies (Album of the Year included) with which her 1994 release, Turbulent Indigo, was rewarded? Or in her induction (belated, she felt) into America's Rock'n'Roll Hall of Fame? And why is it that only the oddest, most unexpected tributes (recently, she accepted a statuette from Sweden's King Carl Gustav, given for outstanding achievement in the field of music) seem to have tickled her fancy? Leading me out on to the patio of a suite within the Bel Air Hotel - close to her home within the jungle-like canyon that comprises Los Angeles' most exclusive postal district - Mitchell attempts to explain why.

It seems that this rehabilitation all started with an honour bestowed upon her by Billboard, the Bible-like trade weekly serving her industry in the US. It was titled The Century Award and was - though doubtless not conceived as such - something of a consolation prize for being undervalued but still around.

"And once I accepted that, a kind of copycat-crime scenario unfolded," she says, searching within the pleated folds of her Issey Miyake outfit for a Bic to light the first of the afternoon's many cigarettes."There was this rash of others which, I felt, didn't do honour to my work. It was as if the establishment-thinking was, 'OK, she's been kind of overlooked - we should give her something'. Yet they didn't quite know why, beyond the fact that other people were doing it. It was as if my time had come again, yet without there being anyone sufficiently knowledgeable around to explain what it is I do, why it is that I might be worthy. So the honours rang hollow. I found myself not grateful. Frankly, the fact of them made me sad."

What might cheer her, then? Well, possibly the fact that a tribute album is in the making, one featuring not the kind of wishy-washy-white-girls-with-guitars that it has been her fate ever to be linked with, but by talents as robust as those of Stevie Wonder, Etta James, Chaka Khan and Janet Jackson. Yes, certainly this pleases Mitchell, who sees it as no coincidence that so many of her celebrity champions - add Seal, jazz diva Cassandra Wilson and, of course, The Artist Formerly Known as Prince to the list of those saying they were influenced by her - are black.

"Comparing new women artists to me robs us both of our individuality. And, while I mean no offence to the personalities involved, it's frequently the case that their art is not innovative and my influence barely perceptible. The blacks though... They make it their own. I say to Prince, 'Wow! that's an interesting chord! Where'd that come from?' And he'll say to me, 'It comes from you!' See, this business is, generally speaking, white male operative. Hence, it likes to lock me in with a lot of girls who've sold a lot more than me, but who don't have nearly the gift."

The white media, too, is guilty of this lazy, generic stereotyping, she feels. "Whereas the black press links me right in there with Miles [Davis] and Santana. It sees someone who's still evolving. It knows a long-distance runner when it sees one" Were she not to have truth on her side, she would be a monster, an ego run riot. As it is - the depth, emotional acuity and linguistic virtuosity of her lyrics, the pioneering musicianship, that voice - she barely begins to state her case.

A new album, released on Monday, is titled Both Sides Now. The best-known version of the title track, written by Mitchell when she was just 21, is cloyingly sweet - the 1970 hit single by Judy Collins. Its author recalls hearing the song reclaimed some time later by veteran cabaret artist Mabel Mercer, then in her seventies and performing at a New York club.

"She was a chansonnier, a storyteller, a mentor of Sinatra. And she just sat there in this black lace gown with a red sash draped on the bias and recounted it... I went to her backstage afterwards and, without identifying myself, said stupidly, 'Oh, but you brought such experience to the words. It really does take an older person to bring them to life.' Whoops! Who was this whippersnapper implying that she was ancient? She was insulted. But it was true. Even though I understood enough to write the lyric when I was young, theatrically speaking it was hard for an audience to relate to a mere girl singing it."

These 35 years on and in its new version, Both Sides Now provides a kind of state-of-the-emotional-nation speech to conclude what is a collection - 2 of classic love songs - ten modern standards originally made famous by such deities as Billie Holiday, Ella Fitzgerald and Nat King Cole - and two of her own compositions revisited. The arrangements, by Vince Mendoza conducting both a 71-piece orchestra and a big-band ensemble, are lush, cinematic, sometimes even Wagnerian. The playing, including solos from jazz luminaries Herbie Hancock, Mark Isham and Wayne Shorter, is peerless. And so are the singer's own vocal performances - closer in essence to Holiday or Sarah Vaughan than to Linda Ronstadt or Carly Simon, peers who have also ventured into the standards market previously.

Above and beyond all this, one thing in particular struck me on first playing the CD. According to the record company hand-out, its choice of material is intended to trace the arc of a modern romantic relationship, "from initial flirtation through optimistic consummation, metamorphosing into disillusionment, ironic despair, and, finally, resolving into a philosophical overview of acceptance and the probability of the cycle repeating itself". And how positively it all starts out... You're My Thrill! At Last! Comes Love! But then, with a full nine songs still to go, love's young dream gets slapped in the face with a wet fish. Track four? Only the accusatory, I'Il-take-the-moral-high-ground-while-you-take-the-moral-lowground bundle of joy that is You've Changed! Hardly a cheery take on things, is it, Ms Misery?

Mitchell giggles delightedly, rocks back and forth in her chair. "Well, that's the nature of romantic love, isn't it?" she says gleefully. "That kind of love is based on insecurity and, the moment it is secured, things go awry. There's the moment of declaration - 'I love you!', 'I love you, too!' - and then, boom! Perfection has been reached and it's all downhill from there. Suddenly, you're in the funny world of 're-lat-ion-ships' [delivering the word, she adopts the loaded-with-meaning tones of the professional counsellor] where things have got to be 'worked on'."

Ah, "work". It was Cher who struck dread into the hearts of fortysomethings by declaring that being in one's fifties sucked. You had to "work" harder and longer for diminishing results, she said, albeit with reference to body maintenance. On this purely superficial level, we might imagine that Mitchell, who modelled as a teenager, loves clothes, and has maintained an elegant public profile these past 30-odd years, will be in agreement. After all, a full quarter century ago, she wrote and sang of youth itself: "Sweet bird you are/ Briefer than a falling star/ All those vain promises on beauty jars/ Somewhere... you must be laughing." We would be wrong, though. Anything but.

"No! No! My fifties are my favourite period since my teens!" she says. "My twenties were just God-awful. I wouldn't go through them again for anything. I lost my daughter [Kilauren, given up for adoption]. Fame hit me, and I was not a fame-seeker. Then I spent my thirties working my way out of the God-awfulness of my twenties. And as for my forties..."

She lights another cigarette, exhales into the accelerating dusk, then motions dismissively with her hand, as if shooing these decades away."Being over 50 is good though." She did, she admits, go through a mini-midlife crisis on passing that particular milestone. "But I didn't go out and buy a sports car, or anything. And I got over the hump. You just do. A lot of stuff gets worked out, blessedly. If you've lived with any sense that you're here to be educated, then hopefully you have achieved some self-knowledge by the time you reach this age. Throughout your youth, there's all that seeking... Who am I? Where's Mr or Ms Right? It takes up so much time and creates so much personal frustration."

The first entrant within the Significant Others category of Mitchell's own CV was Brad MacMath, a photographer with whom she studied at a Calgary art college. Together they moved to Toronto, but the relationship did not survive. Nor did an early marriage, in 1965, to folk singer Chuck Mitchell (though she retained his surname, having been born Roberta Joan Anderson). Later, after settling in Los Angeles, the fledgling star was linked firstly with former Byrds' member David Crosby, who produced 1968's Songs to a Seagull, her debut album, and then another rock musician, Graham Nash.

Those who subscribe to the theory that great art is born out of personal struggle have noted with satisfaction that the ebb and flow of these and other romances coincided with the writing of a series of albums (from Clouds in 1968, through to Don Juan's Reckless Daughter a decade later) wherein she took the confessional songwriting art to new and still unconquered peaks. For evidence, listen to Blue (1970), For the Roses (1972), Court and Spark (1974), The Hissing of Summer Lawns (1975) and Hejira (1976). For Mitchell it was a golden period creatively, and one in which her prolificacy was matched, amazingly, by the very highest, most questing standards, musically and lyrically.

A second marriage, to bassist and record producer Larry Klein, brought a prolonged period of stability and contentment to her life, one lasting from the mid-Eighties through to their break-up after ten years together. Ha! those theorists have exclaimed. The work she produced during their years together (characterised by lyrics which looked outwards, rather than in) was just not as compelling. No matter that it continued to tower above that of most rivals. By self-established standards it was, simply, not as good.

Though divorced now, she and Klein have remained on good terms, and he continues to work on her records. After their parting, she became involved with Don Freed, the son of family friends in Canada. Encountering him briefly three years ago, I gained the impression of a civilised, self-contained man, one able to give his partner the space to be her public self without feeling his own identity to be in any way undermined. A Smile is the Best Facelift, is the title of a song she wrote about their early courtship and, appropriately enough, she grins widely when I ask if they are still together. "Yes. He's lovely. He's wonderful." It is as much as she will volunteer about them or him.

But what about those other facelifts, the non-smiling, very surgical ones? The effects of age on beauty? The increased-effort-for-less-and-less-reward-thing that Cher spoke about? "Oh, I think I always sat on the cusp of beauty anyway," Mitchell shrugs. "No one was ever quite sure if I was beautiful or ugly, pretty or plain. It seemed interpretable. Quite possibly, it changed from day to day. Because I've got a rubber face. Look! It can hold a Garbo-like pose..." she demonstrates. "But then, all of a sudden, it flies off into Edith Bunker [American television's equivalent of the Else Garnett character in our Till Death us Do Part]!" She demonstrates again. "See? There's a comedic streak to my looks, in a way. A gurning tendency.

"Of course, the concept of ageing gracefully is alien here. The elderly are invisible, almost literally; as soon as you get wizened, they hide you away in a home. But there's got to be a better way of fighting that culture than by cutting and snipping. I mean, you can nip and tuck your face and body all you like, have stuff sucked out of here and there, but - well, you can't do anything for your hands and feet! And how's that going to look? Wrinkly old hands and feet, when everything else is pulled tight? "Also, it seems that once people start down that road, they get the appetite to redo and redo. Have surgery once and, I guarantee, you'll find yourself tempted to have it again. In no time at all, you've become this macabre old thing." She shudders. Giggles at the horror of it all. No, absolutely. That route is not for her.

To face the future with equanimity, of course, one must be reconciled to the past. In Mitchell's case, achieving any sense of closure with it came to be dependent on tracing the child she had given over to the Canadian authorities when she herself was just 20 years old. Kilauren Gibb (she takes her surname from the Toronto couple who became her parents) was born from the singer's relationship with MacMath. Of a relationship that ended even before their daughter was born. Of it, she has said, "We were starving artists, hungry and broke. One day I woke up and drove Brad off with my unhappiness." The eventual reunion between the two women, achieved in 1998 and after both sides had made independent efforts to trace each other, was as loaded with emotion as might be imagined. For Mitchell, for example, there was the additional shock and thrill of finding that she was already a grandmother. Gibb, still based in Canada and a former model, was by then divorced from the father of her son, Marlin, now six, and last year had a daughter, Daisy, by a different partner. Commented the singer at the time,"I was prepared for her to hate me, to yell, 'You abandoned me!' I hadn't. I tried desperately to find ways to keep her - I even married a man I didn't love [in order to do so]. I went round in circles but, ultimately, made what I felt at the time was the best decision for her."

Gibb, meanwhile, spoke of the instant bond she felt on first making telephone communication with her mother. "Just to hear her voice was the most calming thing in the world - I guess it's the voice I heard in the womb." In this first flush of excitement, she told reporters of her hope that she and her mother would spend much time together rebuilding their relationship, and might even live together in the same house one day. That in particular would seem to have been overambitious. More recent newspaper reports have talked of Gibb's subsequent rifts with her adoptive parents, a grown-up brother, and many of her friends. As might have been predicted, the reassimilation of the two women after 31 years of separation has not been without recrimination, resentment and pain.

"It's been wonderful and... oh, it's been everything," says Mitchell, a trifle warily now. "I love my grandson. Love him. But my daughter is a difficult girl, you know? Mother daughter - it's a very hard relationship, and she's going to have to forgive me. There's going to have to be a lot of forgiveness before we can really get along. But I expected that. I didn't think it would be all roses. Kilauren is holding a grudge. It's something she's going to have to work through. I can't really help her with it. She's going to have to help herself. We'll... we'll see what happens."

Once upon a time, all of this might have been grist to the lyrical mill. These days Mitchell, who, throughout our time together refers to herself repeatedly as a painter (accomplished and acclaimed, she has exhibited throughout the world) and not a musician, is more circumspect. She is no longer inclined to be confessional or introspective in song.

Nor does she wish to continue the train of social comment that has run through her later albums. With the release of 1998's Taming the Tiger, she fulfilled a contractual obligation to deliver to Warner Brothers only collections of new and original material, thus making possible the cover version concept of Both Sides Now. And, for the time being at least, there will be no new, self-written Mitchell material. "You ask how I feel about America as she is these days. Well, one of the reasons I'm not writing is that I'd rather not say. I can be a very harsh critic, so I've decided to take a sabbatical until I can be nice again!" And she laughs again, but shortly. "I don't want to be a prophet of doom. I don't even want to get started on it all in conversation here and now. But I admit I feel impotent in the face of much of what we've allowed ourselves to become. It's a crass and corrupt world. The sediment has risen to the top. No, I am not without optimism, but that optimism is more of a blind faith than any kind of intellectual certainty."

As daylight fades and the sky above Bel Air turns a deep, expensive blue, we sit for a moment or two in silence. Then I remember the name of performance artist John Kelly. I had read a report of one of his shows, which included him singing - in full Joni drag - an early Mitchell song, The Circle Game, while a rubber chicken revolved endlessly on a turntable. "Tell me about him," I urge her.

Mitchell melts. "It was in this tiny club. I had prepared myself to be roasted, caricatured, but what I found instead was one more kindred spirit. For a start, we have a very kindred wardrobe! For the first set, he was young Joni, for the second Joni in LA. And I liked both dresses! He was very me! Beyond that, it was not... what I expected. It was dreamlike, weird, kind of like being dead and going to your own funeral. I wept in two places. He sang Shadows and Light acappella and, oh! And the audience was so cool. New Yorkers, so correct in their conduct. There was one girl who looked from time to time to see my response, but mostly they acted like I wasn't there. Until, after three encores, it became clear he wasn't coming back. Then they all turned and held their lighters aloft and towards me."

"You see?" I tell her. "You're loved. People live their lives with your music as a soundtrack. I have. The smile I am rewarded with could be that of the DeMolay Sweetheart, 1959.

"Come here," Joni Mitchell commands, rising from her seat. "You need to be given a hug."