Prepare the Cupcakes

1. Preheat Oven: Preheat your oven to 350°F (175°C). Line a 12-cup muffin pan with paper liners.
2. Make the Cupcake Batter: In a mixing bowl, cream together the softened butter and sugar until light and fluffy. This will take about 2-3 minutes with an electric mixer. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
3. Mix Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, and salt.
4. Combine the Wet and Dry Ingredients: Gradually add the dry ingredients to the butter mixture, alternating with the milk. Start and end with the dry ingredients, mixing until just combined.
5. Fill the Cupcake Liners: Spoon the cupcake batter into the lined muffin pan, filling each liner about two-thirds full.
6. Bake: Bake for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Let the cupcakes cool in the pan for 10 minutes, then transfer them to a wire rack to cool completely.

Prepare the Custard Filling

1. Heat the Cream and Milk: In a saucepan, heat the heavy cream and whole milk over medium heat until it begins to simmer. Stir occasionally, but don’t let it boil.
2. Whisk the Egg Yolks and Sugar: While the cream mixture is heating, whisk together the egg yolks, sugar, vanilla, and a pinch of salt in a separate bowl.
3. Temper the Eggs: Slowly pour the hot cream mixture into the egg yolk mixture, whisking constantly to avoid curdling the eggs. Once combined, return the mixture to the saucepan and cook over low heat, stirring constantly, until the custard thickens and coats the back of a spoon (about 5-7 minutes).
4. Cool the Custard: Remove from heat and strain the custard through a fine-mesh sieve to remove any bits of cooked egg. Let it cool to room temperature, then refrigerate until ready to use.

Assemble the Cupcakes

1. Core the Cupcakes: Once the cupcakes have completely cooled, use a cupcake corer or a small knife to remove a portion of the center of each cupcake, creating a small well for the custard filling.
2. Fill with Custard: Spoon or pipe the chilled custard filling into the center of each cupcake, filling the well almost to the top.
3. Seal the Cupcakes: Replace the portion of cupcake you removed, gently pressing it back in place. You can also use a small spoonful of frosting to seal the cupcakes if preferred.

Caramelize the Topping

1. Prepare the Sugar: Sprinkle a thin, even layer of granulated sugar on top of each cupcake.
2. Torch the Sugar: Using a kitchen torch, carefully caramelize the sugar until it turns golden brown and bubbly. If you don’t have a torch, you can place the cupcakes under a broiler on high for 1-2 minutes, watching closely to avoid burning.
3. Cool: Let the sugar topping cool and harden for a few minutes before serving.