A pistachio flavored cake.
A Boston cream pie is a round cake that is split and filled with a custard or cream filling and frosted with chocolate. Although it is called a Boston cream pie, it is in fact a cake, and not a pie. Created by French chef M. Sanzian at Boston's Parker House Hotel, opened in 1855, this pudding/cake combination comprises two layers of sponge cake filled with vanilla custard or crème pâtissière. The cake is topped with a chocolate glaze (such as ganache) and sometimes powdered sugar or a cherry.
The Boston cream pie is the official dessert of the Commonwealth of Massachusetts, declared as such in 1996.