Of all the pop singer/songwriters who surfaced in the 21st century, Sara Bareilles may be uniquely qualified to write the songs for a Broadway musical.

Indebted to tradition without being beholden to it, Bareilles always favors songs so exquisitely sculpted that their craft is never noticed, only felt, so she's a natural fit for Diane Paulus' adaptation of Adrienne Shelly's 2007 indie comedy-drama Waitress.

What's Inside: Songs from Waitress isn't a cast album, it's Bareilles' recording of 12 songs from the production, and the highest compliment that can be paid is that it simultaneously plays as drama and as a sequel to her Grammy-nominated 2013 album The Blessed Unrest.

Bright and open, What's Inside does feel of a piece with her 2010 album Kaleidoscope Heart -- the presence of that album's producer Neal Avron, who sat out The Blessed Unrest, is apparent -- and that warm, colorful sheen is enough to make the album play as pop: simply judged on its surface, it provides tangible pleasures.

The nifty trick Bareilles pulls off on What's Inside is how the songs also contain a double-edge, serving the drama of the story while also playing as pure pop.

Sure, there are flourishes that are pure musical theater -- there's the opening fanfare of "What's Inside." "Never Ever Getting Rid of Me" is Gilbert & Sullivan by way of Todd Rundgren and the show-stopping ballad "She Used to Be Mine" almost seems to conjure a lonely spotlight -- but never once do the songs on What's Inside feel in mere service to a plot.

Taken on their own, they're lively, clever, and bold, and further evidence of Bareilles' versatility, elegance, and wit.