It's called The Cake, and the press materials suggest that Bekah Brunstetter's serious comedy is going to be about, well, a cake. That it turns out to be about guilt, shame, inability to change, and, most pointedly, the differences between the two current Americas testifies to the cunning of this inventive, surprising writer. The Cake is a hoot, and also a full, satisfying meal that clings to the ribs well after its hour and a half. . . .