Joan As Police Woman, Queen Elizabeth Hall, London <!-- none onestar twostar threestar fourstar fivestar -->

Joan Wasser places a mug of steaming tea on the piano as she wanders onstage - a casual kick-off to this South Bank foyer space's opening night. But by the end, Wasser's artistry has marked her out as a star. Until this year, the 35-year-old New Yorker was best known for the company she kept. She has been a member of Antony's Johnsons and Rufus Wainwright's band, and was close to Jeff Buckley. The two albums she has released on the indie label Reveal, under her trio's name, Joan As Police Woman, are strange, off-Broadway art-soul records, spotlighting her extraordinary voice. It is shows like tonight's, though, that are building her a UK following.

Clad in a backless gold gown, Wasser mixes glamour and gaucheness. She gives smoky little laughs, breathes heavily between songs, and introduces "yet another song about obsession". But it is when her voice suddenly vaults and cries out during "The Ride" that her almost feral physicality fully draws you in.

The band showcases her diverse range. "Flushed Chest" is taken with a bluesy roll of the piano and funky smack of drums. The circling bass of "Christobel" is near-techno. The Condoleezza Rice-inspired "Happiness" recalls her past in Boston noise bands.

But it is during "Anyone", a big Seventies piano ballad, that I remember she also worked with Elton John, and the mainstream appeal of her songs' simple, if twisted, sentiments becomes apparent. And then suddenly, in "Real Life", her voice achieves a classical purity of tone and jazzy ease almost unknown in pop, swelling until it seems to merge with the chords of her piano. Beyond punk, sometimes pure musical skill does count, and at this gripping moment it takes Wasser beyond categories.

"We Don't Own It", about her friend, the fine singer-songwriter - and violent suicide - Elliott Smith, sustains the intensity, imagining his final death act, but picked out with pained, quiet reflection. The seated crowd gives a standing ovation. She rewards those fans with a cover of David Bowie's "Sweet Thing", played solo on the guitar, and given scratchy, loose, graceful new life. It brings to an end an exceptional, soul-warming night.