Step 1: Make the Cupcakes

1. Preheat oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.
2. In a bowl, whisk together flour, baking powder, and salt. Set aside.
3. In a separate bowl, beat butter and sugar until light and fluffy.
4. Add eggs one at a time, beating well after each. Stir in vanilla extract.
5. Gradually add the dry ingredients, alternating with milk, mixing just until combined.
6. Divide batter evenly among the cupcake liners.
7. Bake for 18-20 minutes, or until a toothpick comes out clean. Let cool completely.

Step 2: Make the Pastry Cream

8. In a saucepan, heat milk over medium heat until steaming but not boiling.
9. In a separate bowl, whisk sugar, egg yolks, and cornstarch until smooth.
10. Slowly pour the warm milk into the egg mixture, whisking constantly.
11. Return the mixture to the saucepan and cook over medium heat, stirring constantly, until thickened (about 2 minutes).
12. Remove from heat and stir in butter and vanilla extract.
13. Transfer to a bowl, cover with plastic wrap (pressing it onto the surface), and chill until cool.

Step 3: Fill the Cupcakes

14. Use a small knife or cupcake corer to cut a small hole in the center of each cupcake.
15. Spoon or pipe the chilled pastry cream into each hole, filling to the top.

Step 4: Make the Ganache & Top the Cupcakes

16. Heat heavy cream in a saucepan until just steaming. Remove from heat and pour over chopped chocolate.
17. Let sit for 2 minutes, then stir until smooth. Stir in vanilla extract.
18. Spoon or dip each cupcake into the ganache, letting it set before serving.