I am a Boston travel book writer and this is the cake that I make for my out-of-town visitors. Boston Cream Pie is not a pie at all, but a cake that was invented at Boston's Parker House Hotel in 1856. This is my easy version.
Lightly grease two 9 inch -baking pans and line the bases with parchment paper.
Preheat the oven to 350°F.
For the cake: In a bowl cream the butter and sugar. Add the eggs one at a time, beating well after each addition. Add the flour, baking powder and salt. Divide between the two baking pans. Bake for 25 minutes.
For the pastry cream warm the milk and the heavy cream in a medium saucepan. In a large bowl whisk the egg yolks with the sugar until creamy. Add the flour. Add the warm milk to the egg mixture and mix until smooth. Stir in the vanilla. Pour it all back into the saucepan and stir gently until the custard thickens. It should coat the back of a spoon. Remove from the heat. Press a piece of wax paper onto the surface of the custard and let cool in the refrigerator.
For the ganache: combine the heavy cream , butter, vanilla and chocolate in a double boiler. Stir until smooth and thickened.
To assemble the cake: Place one cake on your cake plate. Spread with the cold pastry cream . Top with the second cake and frost the top with the ganache.