Humor and humanity are the icing on ‘The Cake’

In Lyric Stage’s production of Bekah Brunstetter’s play, a same-sex wedding presents a dilemma to a fundamentalist baker played by Karen MacDonald

Karen MacDonald, Chelsea Diehl, and Kris Sidberry in "The Cake" at Lyric Stage Company.Mark S. Howard

Can a wedding cake serve as a bridge across the Red State-Blue State divide, a slice of common ground?

In “The Cake,’’ playwright Bekah Brunstetter suggests that yes, maybe it can, if fortified with the ingredients of mutual goodwill.

That may strike you as facile and overly optimistic, and “The Cake’’ is sometimes guilty of both. But it’s nonetheless pretty hard to resist this heartfelt confection, which is alternately funny and poignant in a production at Lyric Stage Company directed by Courtney O’Connor.

Karen MacDonald portrays Della, a middle-aged North Carolina baker who finds herself torn between her fundamentalist religious beliefs and her innate sense of decency when she is asked to bake a cake for the same-sex wedding of Jen (Chelsea Diehl), the daughter of Della’s deceased best friend.

The versatile and reliably excellent MacDonald demonstrates again that she has few peers in Boston theater when it comes to traversing the territory from comedy to drama and back again — whether from play to play or, as in this case, within the same production. (Next month, MacDonald will star in “The Children,’’ Lucy Kirkwood’s drama about the aftermath of a nuclear disaster, at SpeakEasy Stage Company).

When we first meet Della in her shop, named “Della’s Sweets’’ (the set design is by Matt Whiton), where a crucifix hangs on the wall, she is excitedly preparing to be a contestant on a TV show titled “The Big American Bake-Off.’’ Fans of “The Great British Baking Show’’ and its merciless judge Paul Hollywood will savor the periodic fantasy sequences in which Della is subjected to the increasingly weighty and blunt judgments (voiced by the actor Daniel Berger-Jones) of an unseen, Hollywood-like figure. Part voice of God, part voice of Della’s conscience, he’s a clever device that enables playwright Brunstetter to delineate, and the audience to track, Della’s inner struggle throughout the play.

At first, Della seems like an open book. As she painstakingly puts icing on a cake in her shop, she repeatedly emphasizes the need for a baker of cakes to “follow the directions,’’ with no deviations. Turns out Della takes a similar approach to questions of scripture and morality. She is unaware that Jen — who is now in her early 30s, and whom Della has always loved like a godchild — is gay, and has been living in Brooklyn with her girlfriend, Macy (Kris Sidberry). So Della is taken aback when Jen shows up in her shop to ask that she bake a cake for their wedding.

The flustered baker hems and haws before claiming, in an obvious lie, that her schedule is too full. It is a scene that MacDonald and Diehl handle with consummate skill, Della’s conflicting emotions rippling swiftly across MacDonald’s face while Diehl subtly telegraphs the devastation beneath Jen’s determined smile.

Subsequently, Della battles feelings of guilt, wondering whether she did the right thing. Meanwhile, a rift opens in the relationship between Jen and Macy, who is dumbfounded and incensed that Jen does not appear to feel anger at Della.

As Macy, Sidberry does a skillful job communicating the passion, principles, and loyalty to Jen that lie beneath Macy’s sardonic hipster detachment. As Della’s husband, Tim, Fred Sullivan, Jr. (speaking of reliable excellence) is an asset throughout. Sullivan brings all of his professional aplomb to the execution of a memorable sight gag late in “The Cake.’’ (MacDonald is equally impressive when it comes to a sight gag of her own, earlier in the play).

There are times when the talking points line up too neatly in “The Cake,’’ muddying the play’s point of view and making you wish that Brunstetter, formerly a writer and producer on NBC’s “This Is Us,’’ had dug more deeply into the implications of the issues she raises — by, for instance, exploring the constellation of forces in Della’s life that could lead such a good-hearted person to believe that the simple act of baking a cake for a loved one on her special day was a sin.

But the play’s characters feel real, and Brunstetter was smart to move beyond the usual culture-clash premise to illustrate the interior clash within Jen and Della.

Della starts to finally excavate the pain and unfulfilled need in her own marriage, and discloses a chapter of her personal history that suggests a more complicated, even contradictory view of sexuality than we have been led to assume. Wherever the mode or mood of "The Cake'' shifts, MacDonald skillfully meets the challenge.

As for Diehl, she artfully captures the complexity of her character’s divided self. Jen is balancing her sexual identity with her residual loyalty to the conservative people she grew up with, convinced there is more to them than smart-aleck Northerners acknowledge — yet all-too-aware of the steep price she has paid for the intolerant atmosphere and unexamined assumptions of her upbringing.

THE CAKE

Play by Bekah Brunstetter

Directed by Courtney O’Connor

Presented by Lyric Stage Company of Boston. Through Feb. 9. Tickets start at $25. 617-585-5678, www.lyricstage.com