Make the Cupcakes:

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

Whisk together flour, baking powder, and salt.

In a large bowl, cream butter and sugar until fluffy. Beat in eggs and vanilla.

Alternate adding flour mixture and milk, mixing just until combined.

Divide batter among liners and bake for 18–22 minutes. Let cool completely.

Make the Pastry Cream:

In a saucepan, heat milk until just steaming.

In a bowl, whisk egg yolks, sugar, cornstarch, and flour. Slowly whisk in hot milk.

Return mixture to saucepan and cook over medium heat, whisking constantly, until thickened.

Remove from heat, stir in vanilla and butter. Cover and chill completely.

Make the Ganache:

Heat cream until steaming. Pour over chopped chocolate and let sit 1–2 minutes.

Stir until smooth. Add corn syrup if using. Let cool slightly.

Assemble the Cupcakes:

Use a cupcake corer or small knife to remove centers from cupcakes.

Fill with chilled pastry cream using a spoon or piping bag.

Spoon or dip tops in ganache. Let set before serving.