Make the Cupcakes:

1. Preheat oven to 350°F (175°C) and line a muffin tin with cupcake liners.
2. In a bowl, whisk together flour, baking powder, and salt.
3. In another bowl, beat eggs and sugar until light and fluffy. Add melted butter and vanilla extract, mixing until combined.
4. Gradually add the dry ingredients, alternating with milk, mixing until just combined.
5. Divide batter into the cupcake liners, filling each about ¾ full.
6. Bake for 18-20 minutes or until a toothpick comes out clean. Let cool completely.

Make the Pastry Cream Filling:

1. In a saucepan, heat milk over medium heat until warm (but not boiling).
2. In a bowl, whisk together egg yolks, sugar, and cornstarch until smooth.
3. Slowly pour warm milk into the egg mixture, whisking constantly.
4. Return the mixture to the saucepan and cook over medium heat, whisking constantly, until thickened.
5. Remove from heat, stir in butter and vanilla extract, and let cool completely.

Make the Chocolate Ganache:

1. Heat heavy cream in a saucepan until it just starts to simmer.
2. Pour over chocolate chips in a bowl and let sit for 2 minutes.
3. Stir until smooth and glossy. Let cool slightly.

Assemble the Cupcakes:

1. Cut a small hole in the center of each cupcake and fill with pastry cream.
2. Dip or spread chocolate ganache over the tops.
3. Chill for 30 minutes before serving.