Which doughnut is filled with custard and topped with chocolate, matching the flavors of Boston cream pie?

The doughnut filled with custard and topped with chocolate is the Boston cream doughnut.

This doughnut adapts the flavor combination of Boston cream pie, a dessert made from sponge cake, custard, and chocolate icing. Instead of cake layers, the doughnut uses a yeast-raised or cake-style shell that is split or injected and filled with cream or custard.

The chocolate topping is the visual feature that distinguishes it from many filled doughnuts. The filling may be described as custard, pastry cream, or Boston cream, and recipes differ in sweetness and thickness.

Boston cream doughnuts are often confused with éclairs because both can combine pastry, cream, and chocolate. Their structures differ: an éclair is made from choux pastry, while a Boston cream doughnut is based on fried doughnut dough.