I was  playing around with Wacky Cake again the other day, and decided to make it as a plain cake. I then split it and filled it with custard, and topped it with chocolate icing. Not a true Boston Cream Pie, but a fairly decent imitation, and very easy to make.
The recipe for Wacky Cake is here. Substitute additional flour for the cocoa
The recipe for the custard is here. I only made a half of the recipe.
Chocolate frosting:
1/3 cup cocoa
1 cup icing sugar
enough cream to make it smooth (1-2 tablespoons)