Step 1: Prepare Cookies - Preheat your oven to 180ºC (355ºF). In a medium saucepan, melt the butter over low heat and allow it to cool until it reaches room temperature. Cream together the melted butter, granulated sugar, and dark brown sugar until smooth and slightly fluffy, about 2-3 minutes.

Step 2: Mix Wet Ingredients - Add one large egg and a teaspoon of vanilla extract to the buttery sugar mixture. Mix well until smooth, approximately 1-2 minutes.

Step 3: Mix Dry Ingredients - In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, instant espresso powder, and a pinch of salt. Gradually fold this dry mixture into the wet ingredients until just combined.

Step 4: Shape Cookies - Using a cookie scoop, portion out the dough and roll into balls about 1 inch in diameter. Place on a parchment-lined baking sheet. Chill for 30 minutes.

Step 5: Bake Cookies - Bake for 10-11 minutes until edges are golden brown. Let cool on the baking sheet for a few minutes before transferring to a wire rack.

Step 6: Prepare Mascarpone Cream - In a mixing bowl, combine mascarpone cheese, vanilla extract, confectioners sugar, agave, and heavy cream. Beat on medium speed until stiff peaks form, about 3-5 minutes.

Step 7: Assemble Cookies - Pipe the mascarpone cream onto each cookie and dust generously with cocoa powder.