Preheat your oven to 350°F and line a 12-cup muffin tin with paper liners.

In a mixing bowl, whisk together the flour, baking powder, and salt until combined.

In a separate large bowl, beat the butter and sugar together until the mixture is light and fluffy, about 2 minutes. Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.

Add the flour mixture and the milk to the butter mixture in alternating additions, beginning and ending with the flour mixture, mixing just until incorporated.

Evenly divide the batter among the cupcake liners. Bake for 18 to 22 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Allow the cupcakes to cool completely on a wire rack.

To prepare the pastry cream, whisk the egg yolks, sugar, and cornstarch in a bowl until smooth. In a small saucepan, heat the milk over medium heat until it begins to steam. Slowly pour the hot milk into the egg mixture while whisking constantly to temper the eggs. Pour the mixture back into the saucepan and cook, whisking continuously, until thickened. Remove from heat and stir in the butter and vanilla extract. Strain the cream through a fine-mesh sieve into a bowl, cover with plastic wrap pressed directly onto the surface, and chill in the refrigerator for at least 2 hours until fully cooled.

To make the ganache, place the chopped chocolate in a heatproof bowl. Heat the heavy cream in a saucepan just until it begins to boil. Pour the hot cream over the chocolate and let it sit undisturbed for 5 minutes. Then stir until smooth and glossy. Allow the ganache to cool until it thickens to a pourable consistency, about 15 minutes.

To assemble the cupcakes, use a paring knife to cut a small cone-shaped section out of the center of each cupcake. Fill the holes with pastry cream using a spoon or piping bag. Dip the tops of the filled cupcakes into the ganache, letting any excess drip off. Place the cupcakes in the refrigerator for about 30 minutes, or until the ganache is set.