So how has she done it? Made the leap from pretty-good, pretty-voiced, pretty-faced indie popster to knock-your-socks-off soul singer and classic songwriter? A former teen actress, Jenny Lewis is famed in the US for fronting the band Rilo Kiley. But for all their commercial success, Rilo Kiley's sheeny guitar sounds never hinted at the grown-up brilliance of this, Lewis's second solo album.

Well, a meanie might suggest that it is thanks to the quality of Lewis's collaborators. Check the roll call. For “authenticity” and warm, rootsy vibes, Portland's M. Ward takes on the co-production duties, keeping these arrangements rehearsal-room clear. For rock chops, the Black Crowes man Chris Robinson popped by, as did the Hollywood starlet (and bezzie mate) Zooey Deschanel.

And for ultimate credibility, Elvis Costello guests on the single Carpetbaggers. But that gnarly, urgent singing - surely it's Lewis who is bringing out the best in Costello rather than the other way round?

In any case, what makes Acid Tongue so compelling is that, guests or no, it is clearly Lewis's baby. There is the songwriting for starters, leagues ahead of anything that she has done in the past; the verses in the title track tickle and tease so that you are practically salivating for the chorus.

And, crucially, on all these songs Lewis sings as though she means it. Hers is not a straightahead soul voice, but listen to the way that she sings Bad Man's World - a slinky mêlée of quivering strings and clipped guitars with reverbed cooing that recalls Minnie Ripperton's sublime Les Fleurs - and Lewis's girlishness just serves to supercharge the line “I'm a bad, bad girl”.

The same goes for her country outings - there is no yodelling or Parton-style vocal quivers, but on songs such as Jack Killed Mom, a piano number, Lewis channels the chutzpah of Loretta Lynn. The record closes with the lovely Sing a Song for Them. Carried on a gentle, heart-melting piano refrain, it is so simple it seems a wonder that Carole King didn't write it.

Already there is talk that Acid Tongue might spell the end for Rilo Kiley. But ultimately such speculation is far less interesting than the record itself - a treat from start to finish.

To order Jenny Lewis, Acid Tongue for £11.99 call 0845 6026328 or click here to order online.

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010