This article originally appeared in the first edition of the Ultimate Music Guide published on May 19, 2017.

Charles Mingus was dying when he saw Joni Mitchell in blackface. The great jazz bassist and composer had railed against racism in his autobiography, Beneath The Underdog. But Mitchell's minstrelsy on the cover of Don Juan's Reckless Daughter got his attention. The album's sidelong orchestration of her piano improv, "Paprika Plains", offended him more with its out-of-tune piano, but its content, too, convinced him that Mitchell had "a lot of balls". Mingus had suffered from Lou Gehrig's disease since 1976, a rare, degenerative condition which now left the big, combative man paralysed, and unable to play or compose conventionally. He needed a collaborator to make the music that still filled his head. This white woman from the rock world might just fit the bill.

Mingus couldn't have known how ready Mitchell was for such a request in 1978. The free-flowing structures and fleeting abrasions of The Hissing Of Summer Lawns had flirted with jazz, Hejira had been an intimate musical affair with Weather Report bassist Jaco Pastorius, and Don Juan ... had bust down all the boundaries around her work. But even the increasingly hostile US rock press hadn't grasped how totally she had left folkie Joni behind. By the mid-'70s, she had simply stopped listening to pop, preferring Stravinsky and the electric Miles Davis of In A Silent Way and Nefertiti (her two all-time favourite albums). Yet Mitchell thought of jazz as "sacred and unattainable" music. Mingus's invitation to fully enter the jazz realm almost didn't reach her, as what she called the "normal channels" around her screened his messages at first. After Don Juan, Mingus must have seemed the last straw to some in her exasperated circle.

When Mitchell phoned him, he had a grandly ambitious proposition ready, to adapt TS Eliot's Four Quartets for four simultaneous layers of sound: an orchestra, guitar and bass playing an entirely different sort of music, a formal reading of the poems, and finally, Mitchell singing her earthier distillation of Eliot's words. She gamely bought Eliot's poems to read, but found condensing them an impossible "sacrilege". Undeterred, in April 1978, Mingus rang again, to say he'd written six songs - provisionally and beguilingly titled 'Joni I-VI' - awaiting her lyrics and voice.

Mitchell was "flattered", her then-manager Elliot Roberts recalled in the documentary Woman Of Heart And Mind. Mitchell remembered him warning: "Management begged me not to do it. 'You'll just plummet into obscurity."' She defiantly viewed herself, she told Rolling Stone, as a "musical student", gifted the opportunity to learn from a priceless teacher. Like some bashful wallflower, she'd hung around jazz's pool for three years. Now, she wrote in Mingus' liner notes, "Charlie came by and pushed me in."

Mingus also filled a familiar role in Mitchell's music: the male muse. The erotic aspect may have been minimal this time, but it was still love at first sight. When she met him in his Manhattan skyscraper apartment, his back was turned, and he massively filled a wheelchair she came to view as throne-like. His face was revealed as "glowing, full of the devil... beautiful, open", she said in Woman Of Heart And Mind; to Rolling Stone, she recalled his "sweet giddiness". Not all Mingus's peers would have recognised this gentle, once terrifying giant. The "fearsomely challenging" man she described in Downbeat was closer. But the photos of Mitchell with Mingus and his highly supportive wife, Sue, show a fond, fun relationship. He called her "hillbilly".

The cassette Mingus handed her on that first meeting contained six sung melodies, as physical notation was now beyond him. The plan was for Mitchell to finish these pieces, and complete an LP with two more from his vast songbook. "Goodbye Pork Pie Hat", his 1959 tribute to the late saxophonist Lester Young, was his most famous, lovely tune, and an obvious pick. They spent a pleasant afternoon listening to his other old records. On the East Coast trips that followed, Mitchell would visit his home, where they'd discuss the music's themes and lyrical direction, then retire to work in her apartment at the Regency Hotel.

In every way, she was a long way from Laurel Canyon, and the hippie community she'd once symbolised. Though effectively hired by Mingus, the collaboration was never easy or passive, as Mitchell found herself fully inducted into the jazz world for the first time. A problem in working with a musician 20 years her senior became clear: when Mingus suggested personnel for the recording, she'd never heard of them. Two of the six planned new songs also proved "too idiomatic", she confessed to Downbeat. Though Mingus had been a jazz radical in the '50s, he'd been contemptuous of the next decade's free jazz, and even his most jolting and near-chaotic moments held to verities learned from former employers such as his idol, Duke Ellington. This was black American music with New Orleans roots, which had to swing. Mitchell felt there was nothing she could add to such sounds in 1978. The album's first session, at New York's Electric Lady studios, with Mingus in attendance and a band including his great sax peer Gerry Mulligan, proved her point. "It was closer to what Charlie wanted," she told Downbeat, comparing the session to the album she actually made. It swung more, maybe she even sang better. But it could have been 1960. And what Charlie wanted wasn't enough. "I was after something personal -something mutual - something indescribable," Mitchell wrote.

She kept switching lineups, 'til she got what she wanted: Pastorius back at her right hand on bass, with his Weather Report bandmates and Miles sidemen Wayne Shorter (soprano sax) and Herbie Hancock (electric piano), and Peter Erskine on drums. She felt fully part of this "band of my dreams", she said in Woman Of Heart And Mind. They made music "so braided together that you couldn't take it apart".

By this time, Mingus was unable to say if he approved, or if he'd even heard of Pastorius. Sue Mingus had taken her husband to a faith healer in Mexico, and when Mitchell headed south to visit for 10 days, he could hardly speak. His illness was closing in. Still, Mitchell soaked up his company. Mingus also pointed out key passages in his autobiography, while Sue handed Mitchell home tapes of him talking, filling in more of who he was. What had begun as an active collaboration was becoming a last expression of Mingus' personality, left to Mitchell to finish. "Time never ticked so loudly" as it did in the second half of 1978, she wrote in Mingus's liner notes. She just wanted to complete these songs while Charles Mingus was alive to hear them. Only one, "God Must Be A Boogie Man", was unfinished on his eventual death on January 5, 1979.

Only half of his new melodies made it into the studio (as well as the two Mitchell found "too idiomatic", a "really beautiful" tune floundered on its theme of Mingus's relationship with God, which she couldn't handle). This had become Joni's idea of jazz. A collaboration which had begun with the bassist's maximalist vision of orchestras and epic poems was finally refined to six "audio paintings", as Mitchell described them in her notes, two written by her alone. "God Must Be A Boogie Man" was one of these solo pieces, and became the album's opening tune. Mitchell drew on the first four pages of Beneath The Underdog for its lyrics, which describe Mingus as a soul split in three, alternately watchful, gently loving, and defensively lashing out: "Blind faith to care/Blind rage to kill". The music, meanwhile, made Hejira sound like Sgt Pepper. The intertwining of Pastorius's electric bass and her acoustic guitar was abstracted into a still more intimate duet here. Metallic shards of her instrument, no longer sounding fit for folk, met bass swipes and bullet-crack beats, making up the sparest of sonic palettes. If this music was painterly, to set beside her four evocative, impressionist portraits of Mingus in the LP's lavish gatefold sleeve, then it had "a lot of white canvas", she suggested to Downbeat. Throughout the album, sketched lines and empty space sufficed. This was jazz simmered down to the bone, and beyond.

In a rare emotional confession, Mingus had told Mitchell that the tune she turned into "A Chair In The Sky" was about his trepidation and regrets at impending death. Describing her initial view of him, in his wheelchair in his skyscraper apartment, she imagines him wondering what his "daydreams of Birdland" amount to now, and wryly wishing for more cash and women next time. Hancock and Shorter add decorative ripples, while Joni the singer flexes her Annie Ross fantasies, with some bright, brief scatting, and arcing croons.

Of the two other Mingus/Mitchell originals, "Sweet Sucker Dance" investigates the vulnerability of Mingus in love, adding a measure of Mitchell's own affection: "You're such a sweet love/You're a proud man/You're a treasure". She'd always loved to dance, but rarely found partners among LA's rhythmically stiff singer-songwriters. Mingus is fondly imagined moving with her here. "The Dry Cleaner From Des Moines" is a shaggy dog story about good luck, with a sinuous Shorter solo, and Pastorius-arranged brass stabs. Compared to the earlier music, they sound like an orchestra. "The Wolf That Lives In Lindsey", meanwhile, is a Joni-only tune with no direct Mingus connection, portraying a bad man on the prowl, in Californian canyons haunted by wolf-pack howls.

Tape of a still healthy Mingus talking atmospherically fill some of the album's airy gaps. Styled "raps" in the track listing, he debates his birthdate, has a seconds long doo-wop duet with Mitchell ("I's A Muggin"'), and jokingly imagines death as a cutting contest with his hero Ellington, to see who dies oldest (Duke was 71, Mingus 56). But it's his gorgeously melancholy farewell to Lester Young, "Goodbye Pork Pie Hat", which of course becomes his own elegy. Mingus had passed on reams of personal knowledge about his late friend, but after three months of trying, Mitchell's lyric still wouldn't come. Making the album was liberating, but also frequently confirmed her limitations, and she knew she was no biographer. She could only respond to her own experience. And, shortly after her return from Mexico, the New York night gave her what she needed, as she wandered out of the subway with the album's conga player, Don Alias. They saw two young black kids doing what in retrospect sounds a lot like body-popping, to jukebox jazz coming through the door of the Pork Pie Hat, a jazz club covered in photos of Lester Young. This unlikely apparition let her end the jazz she made with Mingus with a verse set in the present, which looked to the future. And he would have been pleased that it really swung.

Even rock journalists theoretically sympathetic to the album didn't get it, on its June 1979 release. "Mingus, unfortunately, doesn't enhance his legend," judged MM's Michael Watts, "and it diminishes hers." Arare bright spot came in US jazz bible Downbeat, which declared: "This is a wonderful record ... Even in those moments when the deed fails, the thought carries the day." It's an album that can sound as if it's not all there, with whatever last threads of melody Mingus provided sounding ephemeral next to the climactic tune from his '50s pomp. Joni's love for the Mingus she met, and determination to honour him with original work, creates music that sometimes seems about to disappear.

Mitchell had put a lot into Mingus, and really hoped it would be accepted. Instead, neither rock nor jazz radio played it, and it became her worst-selling record of the decade. In The Times years later, she declared herself "stricken from the history of rock'n'roll in America" by its release. She had gone way out on a limb. Now the hostile '80s were coming, and Mitchell would have to work her way back.