This peanut butter Boston cream pie is a light and spongy vanilla genoise layered with a peanut butter pastry cream and topped with a rich chocolate ganache.
In a medium pot, whisk together the sugar, flour, and salt.
Slowly whisk in the milk, then cook the mixture over medium-high until bubbling and thick.
Whisk some of the hot milk mixture into the yolks, to warm them, then add the warmed yolks into the pot, and cook over medium-low flame, whisking, until bubbling and thick.
Stir the peanut butter and vanilla extract into the pastry cream, then strain into a heat-safe bowl, place plastic wrap over the surface, and chill.
Preheat the oven to 350 degrees F.
Combine the eggs and the remaining sugar in a mixing bowl, and set over a large bowl of very hot water.
Mix with your hand until warm to the touch, then remove from the heat and whip on high speed until very fluffy, and batter falls from the beater in long, thick ribbons.
Mix a little of the batter into the melted butter, and then pour back into the mixing bowl and fold until combined, taking care not to deflate the air from the batter.
Bake in an ungreased 8- or 9-inch round cake pan for 30 minutes, or until a toothpick inserted in the thickest part of the cake comes out clean.
Place one (fully cooled) genoise layer on a serving plate.
Spread the peanut butter pastry cream filling all over the cake in an even layer.
Top with the remaining genoise layer, and drizzle with chocolate ganache.