“Waitress,” a new musical from director Diane Paulus, not ironically given its storyline, is like a pie. Specifically, it’s like a tart blackberry slice which, while questionable at first, sweetens with time and becomes addictive (imagine reaching for a second slice...and a third). Based on Adrienne Shelly’s 2007 film of the same name, this musical running at the American Repertory Theater until Sept. 27th follows waitress and expert pie baker Jenna (the always spectacular Jessie Mueller, but more on that later) as she tries to leave an abusive husband and make her life what she wants it to be.

The set of Joe’s Diner, a tiny restaurant off Highway 27 where Jenna works with bookish Dawn (Jeanna de Waal) and tough-love Becky (Keala Settle) at first seems cutesy, nothing more, but soon becomes the background for a story of perseverance and self-reliance. Customers blend into the diner, complete with sticky metal napkin holders and a grouchy frycook, Cal (Eric Anderson). The stage itself is framed with a piecrust, complete with a cherry pie lattice screen which comes down in between acts. Jenna even thinks to herself in pies, dreaming up ingredient combinations which appear on the diner’s daily specials blackboard. This pie motif continues to pop up in script and song—the audience is beat over the head with it—but, in time, its saccharine crust flakes off to reveal the tender, moving center within.

That heart comes from pop phenom Sara Bareilles’ score, which, while reminiscent of her previous work, reaches a new emotional depth. Indeed, in the playbill Paulus comments on choosing Bareilles for this project, writing that Bareilles’ songs “capture...the humanity of all the characters in this story with her signature mix of humor and heartache.” Paulus’ words are true: the songs are catchy and powerful, with careful instrumentation and thoughtful lyrics. “She Used to Be Mine,” a ballad from the faster-paced second act of the musical, is a prime example, thanks in part to Mueller’s soft twang, which she has carried over and honed from her previous role as Carole King in “Beautiful: The Musical.” Coupled with a poignant melody, the lyrics simultaneously connect listeners to Jenna’s struggles and let them reflect on how their own lives have unfolded. Jenna becomes everyone, nostalgic for the past and trying to come to grips with moving on, letting the present be enough: “She’s imperfect, but she tries / … She is broken and won’t ask for help / She is messy, but she’s kind / She is lonely most of the time / She is all of this mixed up and baked in a beautiful pie / She is gone, but she used to be mine.” Mueller’s powerful performance makes it clear that although Jenna sings to the audience here, she really sings for herself.

Jenna’s realization that she has the power to change her life for the better ultimately enables “Waitress” to succeed; the show becomes part of a larger conversation about finding inner strength. Paulus, Bareilles, and book writer Jessie Nelson have written about the integrity and courage exemplified by Jenna, in connection with a growing national dialogue about domestic violence. Indeed, the playbill highlights the partnership between the A.R.T. and Harvard’s Office of Sexual Assault Prevention & Response. In “Waitress,” though, Jenna ultimately wins because of her own self-acceptance, not merely because of guidance from caring figures, like Joe, the perennial elderly and particular patron (Dakin Matthews), and love interest Dr. Pomatter (Drew Gehling). In fact, Jenna ultimately decides that running away with Dr. Pomatter would not give her the life she wants, and she ends the affair on her own terms. In the end, Jenna sprinkles in a message of self-confidence to complete “Waitress’” recipe for success.

—Staff writer Melissa C. Rodman can be reached at melissa.rodman@thecrimson.com. Follow her on Twitter @melissa_rodman.