America Ferrera, James Lapine

Few love words as passionately as Broadway's master composer-lyricist Stephen Sondheim, but there's one word that makes him cringe: "Hummable," a quality some (erroneously) find lacking in his challenging, rewarding scores. "Drives me up the wall," he growls.

Which is why it's such an ironic delight when Sondheim performs as part of a new staging of his autobiographical "Opening Doors" production number (from the initially flop musical Merrily We Roll Along), playing a producer who bullies a team of young songwriters to conjure a "humm-umm-able melody."

In HBO's fascinating documentary portrait Six by Sondheim (Monday, 9/8c), longtime collaborator James Lapine assembles an intricate and revealing mosaic of vintage and recent interviews with the always quotable Sondheim. Lapine uses a half-dozen of Sondheim's most notable songs as a springboard for a biographical study that's contemplative, analytical and transcendentally emotional. (Lapine also directed the "Opening Doors" segments, featuring Smash's Jeremy Jordan, Glee's Darren Criss and America Ferrara as the show-biz hopefuls.)

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The playlist includes Sondheim's one breakout hit song, A Little Night Music's "Send in the Clowns," represented in an eclectic YouTube all-star mash-up leading into a pensive cover by Audra McDonald (who was the high point of last week's The Sound of Music); "Something's Coming" from West Side Story (for which he wrote the lyrics when he was still in his twenties), performed by the original Tony (Larry Kert) in a clip from a '50s Sunday-morning show Look Up and Live; "Being Alive" from his revolutionary musical Company (sung by Dean Jones in a key scene from D.A. Pennebaker's legendary documentary about the making of the original cast album); the Follies anthem "I'm Still Here," given a pretentious performance-art gender-reversal spin by Jarvis Cocker (strikingly filmed by Todd Haynes); and the euphoric "Sunday" from the Pulitzer-winning Sunday in the Park With George. Theater fans will also thrill to rare footage of Ethel Merman as the original Mama Rose of Gypsy — Sondheim has a great anecdote about the famously profane diva that gets a laugh every time — among other archival gems.

Throughout, as Lapine interweaves interviews from different eras (and wildly different looks, hairstyles and wardrobes), Sondheim exults in the "agonizing fun" of his craft. We can only marvel at the results.

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