From the iconic Mom’s apple variety to the cherry slices served up in Twin Peaks, the American reverence for pie is something of a mystery to those of us across the Atlantic. Sara Bareilles’ musical (based on the 2007 film by Adrienne Shelly) goes quite a way towards indoctrinating us in the spirit of pie-philia, until the final phase proves too sugary.

Jenna is doubly trapped, as a waitress and cook in a pie diner and in a loveless marriage to arrogant drunkard Earl. When she discovers she is pregnant, it’s only natural (at least in musical theatre terms) that she should embark on an affair with her gynaecologist. She also hears of a pie-cooking contest with the kind of big-money prize that would enable her and her child-to-be to make a life of their own away from the irksome Earl. In Diane Paulus’ production (she also directed the US stage première in 2015), Jenna’s story interweaves with those of her fellow waitresses, lippy Becky who unexpectedly hooks up with the diner’s manager Cal, and timid Dawn who is more surprised than anyone to find herself passionately involved with an eccentric accountant.

Bareilles’ tunes are for the most part bouncy and propulsive, with Katharine Woolley’s band punching them along, drummer Ed Carlile in the driving seat with a nice, tight snare sound (augmented on one number by an outburst of flamenquista clapping). The musical idiom doesn’t incline in any particular direction: an astute blend of stage-musical and more-or-less-pop. American Idol alumna Katharine McPhee, in common with most of the principals, has a semi-nasal contemporary singing voice, but she and her fellows don’t toss their power around aimlessly: the singing is thankfully free of melisma, and those high, sustained, climactic notes are pure, with only a touch of vibrato on the lead-out.

The weakest singing voice is that of Jack McBrayer (of 30 Rock and Conan O’Brien fame) as Dawn’s beloved Ogie, but the mere fact of his being Jack McBrayer more than counterbalances any reservations. He is a master of rural American grinning, gormless gee-whizzery, and his energy and dedication take him where melodic precision doesn’t quite reach. Other standout supporting performances come from Shaun Prendergast as the irascible Joe, owner of the diner, and Kelly Agbowu as the sardonic Nurse Norma, who at one point on press night almost corpsed both McPhee and David Hunter as her appealing OB-GYN lover.

All in all, the show had pretty much won me over by the interval: it contains a palpable strain of sentiment, but not so strong as to trip up the narrative. Alas, the second act heads squarely in the direction so thankfully absent hitherto; a succession of ballads, and after setting up a target of female fulfilment, a plummeting cop-out when Jenna is unable to enter the competition, and ultimately finds the self-confidence to dump Earl in... yes... motherhood. The happy ending feels calculated rather than organic, and in the end that near-understanding of all that pie can stand for is spoiled by a sickly final course.

Written for the Financial Times.