Preheat the oven to 350°F (175°C). Line a muffin tin with cupcake liners.

In a large mixing bowl, cream together the softened butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

In another bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the butter mixture, alternating with milk, starting and ending with the flour mixture. Mix until just combined.

Pour the batter evenly into the lined muffin tin, filling each liner about ⅔ full. Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean. Let the cupcakes cool completely on a wire rack.

To make the pastry cream, heat the milk and half of the sugar in a saucepan over medium heat until just simmering. In a separate bowl, whisk together the egg yolks, cornstarch, and the remaining sugar until smooth.

Slowly pour the warm milk mixture into the egg yolk mixture, whisking constantly. Return the mixture to the saucepan and cook over medium heat, stirring until thickened, about 5-7 minutes. Remove from heat and stir in the butter and vanilla extract. Transfer the pastry cream to a bowl, cover with plastic wrap, and let it cool completely.

Once the cupcakes are cool, use a pastry bag or a small knife to create an opening in the center of each cupcake. Fill each cupcake with the chilled pastry cream.

For the chocolate glaze, heat the heavy cream in a saucepan until it begins to simmer. Remove from heat and add the chocolate chips, stirring until melted and smooth.

Drizzle or dip the filled cupcakes in the chocolate glaze and allow them to set.