Directions:
Cupcakes: Preheat your oven to 350°F (175°C). Mix flour, sugar, baking soda, and baking powder in a large bowl. Add butter, egg whites, vanilla extract, sour cream, and milk; beat until smooth. Fill cupcake liners 2/3 full and bake for 18-20 minutes. Cool on a wire rack.
Pastry Cream Filling: Heat heavy cream until it simmers. Whisk egg yolks, sugar, and cornstarch. Gradually add hot cream to the egg mixture, then return to heat. Stir until thick, remove from heat, add vanilla, cover, and chill.
Chocolate Ganache: Heat heavy cream to a simmer and pour over chopped chocolate. Let sit, then stir until smooth.
Ganache Layer: Once the cupcakes are cooled, remove a center piece from each. Pour a teaspoon of ganache into each hole and freeze briefly to set.
Assembly: Fill the cupcakes with chilled pastry cream over the set ganache layer. Dip each cupcake top into the remaining ganache. Let set
