Preheat oven to 350°F and line a muffin tin with cupcake liners.
In a bowl, whisk flour, baking powder, and salt together.
In another bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, then mix in vanilla.
Alternate adding dry ingredients and milk until the batter is smooth.
Fill liners about 2/3 full and bake 18–20 minutes, until a toothpick comes out clean. Cool completely.
Brush cupcakes with cooled espresso.
Beat mascarpone, heavy cream, and powdered sugar until soft peaks form.
Pipe or spread mascarpone cream over cooled cupcakes.
Dust with cocoa powder before serving.