Preheat oven to 350°F (175°C). Line a muffin tin with cupcake liners.
Whisk together flour, baking powder, baking soda, and salt.
Cream together sugar and butter until light and fluffy.
Add eggs one at a time, then vanilla. Mix in sour cream and espresso.
Gradually add dry ingredients, mixing until just combined.
Fill cupcake liners ¾ full with batter. Bake for 18-20 minutes, or until a toothpick comes out clean. Cool completely.
Combine espresso and coffee liqueur. Pierce the top of each cupcake several times with a fork and brush with coffee soak.
Beat mascarpone, powdered sugar, and vanilla until smooth.
In another bowl, whip heavy cream to stiff peaks. Fold whipped cream into mascarpone mixture.
Pipe or spread frosting on each cupcake. Dust with cocoa powder and garnish with chocolate curls.
