Preheat oven to 350°F and line a muffin tin with cupcake liners.
In a bowl, whisk together flour, baking powder, and salt.
In another bowl, cream the butter and sugar until light and fluffy. Beat in eggs and vanilla bean paste.
Alternate adding the flour mixture and milk to the butter mixture, starting and ending with flour.
Fill liners two-thirds full and bake for 18–20 minutes or until a toothpick comes out clean. Let cool.
For the custard: Heat heavy cream until just simmering. In a bowl, whisk egg yolks with sugar, then slowly whisk in warm cream.
Cook custard over low heat, stirring until thick enough to coat the back of a spoon. Let cool slightly.
Scoop out a small well in each cupcake and fill with custard. Chill for 30 minutes.
Sprinkle sugar on top of each cupcake and caramelize using a kitchen torch until golden and crisp.