Preheat oven to 175°C (350°F) and line a cupcake pan with liners.

In a bowl, mix flour, baking powder, and salt.

In another bowl, beat butter and sugar until light and fluffy. Add eggs and vanilla extract and mix well.

Gradually combine wet and dry ingredients, alternating with milk until smooth.

Fill cupcake liners 2/3 full and bake for 18–20 minutes until a toothpick inserted comes out clean.

Cool cupcakes completely on a wire rack.

For the custard, heat milk until simmering. In a bowl, whisk sugar, egg yolks, cornstarch, flour, and salt.

Slowly add hot milk to the egg mixture while whisking to temper the eggs.

Return mixture to the saucepan and cook until thickened, stirring constantly.

Remove from heat, stir in vanilla and butter, then cover and refrigerate until cooled.

Prepare the ganache by heating cream and pouring it over chocolate. Stir until smooth, then mix in vanilla and optional corn syrup.

Fill cooled cupcakes with custard, then top with chocolate ganache before serving.