In a bowl, cream together the soft butter, white sugar, and brown sugar until light and fluffy. Add the beaten half egg and mix well. Pour in the espresso and stir until fully combined. Add the flour, baking powder, and baking soda and mix just until a soft dough forms. Do not overmix.

Preheat the oven to 180°C (top/bottom heat). Scoop the dough into 6 equal portions and place them on a lined baking tray with space in between. Bake for 11 minutes until the edges are set but the centers are still soft.

As soon as the cookies come out of the oven, they may have spread. Use a glass or spoon to gently push them back into a round shape while they’re still hot. Let them cool completely.

In a bowl, mix mascarpone, powdered sugar, vanilla extract, the remaining half egg, and espresso powder until smooth and creamy. Do not overmix, it should stay thick and fluffy.

Pipe or spoon the mascarpone frosting onto the cooled cookies in a swirl, covering the entire surface. Finish by dusting with cocoa powder through a sieve.