Preheat your oven to 180°C (350°F). Line a muffin tin with cupcake liners.
Cream together the softened butter and sugar in a mixing bowl until light and fluffy.
Add in the eggs one at a time, mixing well after each addition.
Slowly incorporate the espresso mixture, blending until combined.
In another bowl, whisk together the all-purpose flour, cocoa powder, and baking powder.
Gradually add the dry mixture to the wet ingredients, mixing just until combined. Do not overmix.
Divide the batter evenly among the cupcake liners, filling each about two-thirds full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Let cupcakes cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.
Beat the heavy cream in a clean bowl until soft peaks form.
Mix the mascarpone cheese and sifted confectioners' sugar until smooth.
Gently fold the whipped cream into the mascarpone mixture to create a light and fluffy frosting.
Once cupcakes are completely cool, pipe or spread the mascarpone frosting on top.
Dust with cocoa powder and sprinkle dark chocolate shavings over the frosting for decoration.