Preheat your oven to 350°F (175°C). Line a muffin tin with cupcake liners or grease it lightly.

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large mixing bowl, use a hand mixer or stand mixer to cream the softened butter and sugar together until light and fluffy, about 2–3 minutes.

Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.

Alternate adding the dry ingredients and milk to the wet ingredients, beginning and ending with the dry ingredients. Mix just until combined.

Divide the batter evenly among the prepared cupcake liners, filling each about ⅔ full.

Bake in the preheated oven for 18–20 minutes, or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.

In a medium saucepan, heat the milk over medium heat until it begins to simmer. Remove from heat.

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

Gradually whisk half of the hot milk into the egg mixture to temper it, then pour the mixture back into the saucepan.

Cook over medium heat, whisking constantly, until the mixture thickens and comes to a boil, about 5–7 minutes.

Remove from heat and stir in the butter and vanilla extract until smooth.

Transfer the pastry cream to a bowl, cover with plastic wrap (pressing it directly onto the surface to prevent a skin from forming), and chill in the refrigerator for at least 2 hours.

Heat the heavy cream in a small saucepan or microwave until just simmering.

Pour the hot cream over the chocolate chips in a heatproof bowl. Let sit for 2–3 minutes, then whisk until smooth and glossy.

Let the ganache cool slightly to thicken before using.

Once the cupcakes are completely cool, use a small knife or cupcake corer to cut a hole in the center of each cupcake, leaving a small border around the edges.

Fill a piping bag with the chilled pastry cream and pipe it into the hollowed-out centers of the cupcakes.

Dip the tops of the cupcakes into the chocolate ganache or spoon the ganache over the tops, spreading it gently to cover.

Allow the ganache to set before serving.