What is the classic filling of a Boston cream doughnut?

The classic filling of a Boston cream doughnut is vanilla custard.

A Boston cream doughnut is a round, yeast-risen doughnut filled with vanilla custard, also called crème pâtissière, and topped with chocolate icing or glaze. The custard is the defining interior component, while the chocolate topping links the doughnut to Boston cream pie.

Boston cream pie is actually a cake made from layers of sponge cake, custard, and chocolate. It was developed in Boston and became Massachusetts’s official state dessert in 1996. The doughnut version adapts those same flavor combinations into a portable fried pastry.

The filling is sometimes loosely called cream, which can create confusion with whipped cream or Bavarian cream. Those may appear in related doughnuts, but they are not the classic Boston cream formula. Chocolate pudding and raspberry jam are also possible doughnut fillings, but neither is traditional here.

Massachusetts designated the Boston cream doughnut its official state doughnut in 2003, making it one of the most prominent regional doughnut varieties in the United States.