Preheat your oven to 180ºC (355ºF). Line two baking sheets with parchment paper.

In a large mixing bowl, combine melted butter with granulated and brown sugar. Beat until creamy and smooth.

Add the egg and vanilla extract to the mixture, mixing until well combined.

In a separate bowl, whisk together all-purpose flour, baking powder, baking soda, instant espresso powder, and salt. Gradually fold this into the wet mixture.

Portion out the dough into balls and chill in the refrigerator for 30 minutes.

Bake the cookies for about 10–11 minutes, until edges are golden and centers are soft.

In a separate bowl, mix mascarpone cheese, heavy cream, vanilla extract, and confectioners' sugar until stiff peaks form. Chill until ready to assemble.

Pipe the mascarpone topping onto each cookie and dust with cocoa powder.