1️⃣ Preheat the oven:
Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.

2️⃣ Make the cupcake batter:
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt. Add the softened butter, eggs, milk, and vanilla extract. Beat with an electric mixer until the batter is smooth and well combined.

3️⃣ Bake the cupcakes:
Divide the batter evenly among the cupcake liners, filling each about ⅔ full. Bake 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, then transfer to a wire rack to cool completely.

4️⃣ Prepare the custard filling:
In a medium saucepan, whisk together the milk, egg yolks, sugar, and cornstarch. Cook over medium heat, stirring constantly, until the mixture thickens, about 5-7 minutes. Remove from heat and stir in the vanilla extract. Transfer the custard to a bowl, cover with plastic wrap directly on the surface to prevent a skin from forming, and chill in the refrigerator until cool.

5️⃣ Make the chocolate ganache:
Heat the heavy cream in a small saucepan over medium heat until it just begins to simmer. Pour the hot cream over the chopped chocolate in a heatproof bowl. Let sit for 5 minutes, then stir until smooth and glossy. Allow the ganache to cool slightly.

6️⃣ Assemble the cupcakes:
Use a small knife or cupcake corer to cut a small hole in the top center of each cupcake. Fill the holes with the chilled custard.

7️⃣ Top with ganache:
Spoon or drizzle the chocolate ganache over the top of each cupcake, allowing it to slightly drip down the sides.

8️⃣ Serve:
Let the ganache set slightly before serving. Store leftovers in the refrigerator.