Melt 1 stick of unsalted butter and let it cool until room temperature. In a large mixing bowl, combine with ½ cup granulated sugar and ½ cup dark brown sugar, whisking until blended. Add 1 large egg and 1 teaspoon of vanilla extract, mixing until smooth. In another bowl, whisk together 1 ½ cups all-purpose flour, 1 teaspoon baking powder, ½ teaspoon baking soda, 2 tablespoons instant espresso powder, and ¼ teaspoon salt, then gradually fold this mixture into the wet ingredients until just combined.

Using a cookie scoop, portion the dough into approximately 11 balls and roll each one to form smooth spheres. Place the cookie dough balls on a parchment-lined baking sheet. Cover with plastic wrap and chill in the refrigerator for 30 minutes.

Preheat your oven to 180°C (355°F). Once chilled, place 6 cookie balls on a lined baking sheet, leaving space for spreading. Bake for 10-11 minutes, until puffed up and lightly golden. Allow cooling on the baking sheet before transferring to a wire rack.

In a mixing bowl, combine 1 cup of mascarpone cheese, 1 teaspoon of vanilla extract, ½ cup of confectioners' sugar, 1 tablespoon of agave syrup, and ½ cup of heavy cream. Use an electric mixer to whip on low speed, then medium, until stiff peaks form. Keep chilled until ready to use.

Once cookies are cooled, use a piping bag or spatula to spread and swirl the mascarpone cream on top of each cookie. Dust with cocoa powder and serve fresh.