1. Preheat your oven to 350°F (175°C).
2. In a bowl, cream together the softened butter and granulated sugar until light and fluffy.
3. Add the egg and vanilla extract, mixing until well combined.
4. In another bowl, whisk together the flour and cocoa powder.
5. Gradually add the dry ingredients to the wet mixture, mixing until just combined.
6. Fold in the cooled espresso until the dough is smooth.
7. Drop spoonfuls of dough onto a baking sheet lined with parchment paper.
8. Bake for 10-12 minutes or until the edges are set.
9. Let the cookies cool completely.
10. In a separate bowl, mix the mascarpone cheese and powdered sugar until smooth.
11. Spread the mascarpone mixture on top of each cookie and dust with cocoa powder.

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