Heat the oven to 180°C/350°F. Line two cupcake baking trays with 18 paper liners. (if using a cupcake maker, just line with cupcake cases and heat until ready).
In a mixing bowl whisk the butter and sugar for 2-3 minutes until light and fluffy. Add the eggs, one at a time, beating well after each addition.
In a separate bowl sift together the flour, cocoa and baking powder. Add the flour mixture alternately with the cold coffee mix to the creamed butter, and mix all the ingredients until just combined
Divide the batter into the prepared cupcake tins ( if using a cupcake maker you'll have o make 2 batches) and bake for 20 minutes or until a toothpick inserted in the middle comes out clean.
Leave the cupcakes in the tin for 5 minutes before placing them on wire racks to cool completely.
With an electric mixer on medium speed, whisk heavy cream until stiff peaks form (be careful not to overbeat the cream).
In another bowl, whisk together mascarpone and confectioners' sugar until smooth.
Gently fold whipped cream into mascarpone mixture until completely incorporated.
Transfer the tiramisù frosting into a piping bag and top each cupcake.
Decorate with cocoa powder and chocolate shavings.