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

Whisk together the flour, sugar, baking powder, and salt in a large bowl.

In another bowl, beat the softened butter until creamy. Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with the milk. Mix until just combined.

Divide the batter evenly among the prepared cups, filling each about two-thirds full. Bake for 18-20 minutes until golden and a toothpick inserted in the center comes out clean. Allow the cupcakes to cool completely.

For the pastry cream, heat the milk in a medium saucepan over medium heat until it just begins to steam.

In a separate bowl, whisk together the egg yolks, sugar, and cornstarch until smooth and pale yellow.

Slowly pour half the hot milk into the egg mixture while whisking constantly. Then, pour everything back into the saucepan.

Cook over medium heat, whisking constantly, until the mixture thickens and bubbles. Remove from heat and stir in the butter and vanilla extract. Refrigerate until completely cold.

For the ganache, place the chocolate chips in a heatproof bowl. Heat the heavy cream until it just begins to simmer. Pour the hot cream over the chocolate and let it sit for two minutes, then stir until smooth.

Using a paring knife, cut a small cone-shaped piece from the center of each cooled cupcake. Fill each cavity with chilled pastry cream and replace the tops.

Spoon the chocolate ganache over each cupcake and refrigerate for at least 30 minutes before serving.