Prepare your workspace and ingredients. Preheat oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners. Allow butter, eggs, and milk to come to room temperature for best results.
Make the custard filling first. In a heatproof bowl, whisk together egg yolks and sugar until pale and slightly thickened. Heat the heavy cream in a saucepan until it just begins to simmer (do not boil), then slowly pour into the egg mixture while constantly whisking.
Cook the custard properly. Return the mixture to the saucepan and cook over low heat, stirring constantly, until it reaches 175°F on an instant-read thermometer and coats the back of a spoon. Immediately strain through a fine-mesh sieve, stir in vanilla and salt, then cover with plastic wrap directly on the surface and refrigerate.
Prepare the cupcake batter. In a medium bowl, whisk together flour, baking powder, and salt. In a separate large bowl, beat butter and sugar with an electric mixer until light and fluffy, about 3 minutes. Add eggs one at a time, beating well after each addition, then mix in vanilla.
Combine wet and dry ingredients carefully. Gradually add the flour mixture to the butter mixture in three additions, alternating with the milk, beginning and ending with the flour. Mix just until incorporated after each addition – overbeating will result in tough cupcakes.
Bake the cupcakes until just done. Divide batter evenly among the cupcake liners, filling each about ⅔ full. Bake for 18-20 minutes or until a toothpick inserted in the center comes out clean. Allow to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.
Create space for the filling. Once cooled, use a small knife or cupcake corer to remove the center of each cupcake, creating a well about 1 inch in diameter and 1 inch deep. Save the cake tops for later.
Fill each cupcake generously. Remove custard from refrigerator and spoon or pipe it into the wells of each cupcake. Cut the reserved cake tops to create a thin “lid” and place over the filling.
Make the vanilla frosting. Beat butter until creamy, then gradually add powdered sugar, vanilla, and enough heavy cream to achieve a smooth, spreadable consistency. Pipe or spread a thin layer on top of each cupcake.
Create the signature brûlée topping. Just before serving, sprinkle each frosted cupcake with a thin, even layer of granulated sugar. Use a kitchen torch to carefully caramelize the sugar until it melts and turns amber (alternatively, place under a broiler for 1-2 minutes, watching carefully to prevent burning).
Allow the sugar to harden before serving. Wait 1-2 minutes for the caramelized sugar to cool and form a crisp, crackable top before serving.