Preheat your oven to 180ºC (355ºF).

Melt the butter and let it cool to room temperature. Combine melted butter, granulated and dark brown sugars until creamy. Add egg and vanilla extract; blend well.

In a separate bowl, whisk together flour, baking powder, baking soda, espresso powder, and salt. Gradually fold dry ingredients into the wet mixture until just combined.

Portion the dough into balls and place on a parchment-lined baking sheet. Chill in the refrigerator for about 30 minutes.

Bake for 10-11 minutes, until edges are lightly golden and centers remain soft. Let cool briefly before transferring to a wire rack.

In a mixing bowl, beat mascarpone cheese, vanilla extract, heavy cream, and confectioners sugar until stiff peaks form. Chill mixture.

Pipe mascarpone cream onto each cooled cookie and dust with cocoa powder.