Bake the Cupcakes:

• Preheat oven to 350°F (175°C). Line a cupcake pan with liners.
• Prepare the cake batter according to the package directions.
• Fill liners ¾ full and bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
• Let the cupcakes cool completely.

Make the Pastry Cream:

• In a saucepan, heat milk and heavy cream over medium heat until steaming.
• In a separate bowl, whisk together sugar, cornstarch, and egg yolks.
• Slowly pour the hot milk into the egg mixture, whisking constantly.
• Return mixture to the saucepan and cook over medium heat, stirring, until thickened (about 2 minutes).
• Remove from heat, stir in vanilla and butter, then cool completely.

Fill the Cupcakes:

• Cut a small hole in the center of each cupcake (using a knife or piping tip).
• Spoon or pipe the cooled pastry cream into the hole.

Make the Chocolate Ganache:

• Heat heavy cream in a small saucepan until it begins to simmer.
• Pour over chopped chocolate and let sit for 1 minute. Stir until smooth.
• Let cool slightly, then spoon over each cupcake.

Serve & Enjoy:

• Allow ganache to set for about 15 minutes before serving.