Preheat your oven to 350°F.
While the oven is preheating, cream your butter, brown sugar, and granulated sugar together in a large mixing bowl using an electric hand mixer or stand mixer. Mix for 5 minutes, or until smooth and creamy
Once the butter and sugars are homogenous, add the eggs and vanilla. Mix for another 2 minutes to incorporate the new ingredients.
Reduce the speed of your hand mixer and gently whisk in the flour, baking powder, baking soda, and espresso powder. The cookie dough will appear a little crumbly at first, but will come together after a minute or two.
Use a cookie scoop or your hands to divide the cookie dough into 12 evenly sized balls. Flatten the dough a little bit to shape the dough into discs and place 6 on a 9x13 inch metal baking sheet.
Bake your cookies for 11 minutes and then allow them to cool in the fridge for an hour.
While your cookies are cooling, prepare your frosting by whisking the powdered sugar, mascarpone, heavy cream, and vanilla together in a medium sized bowl with your hand mixer. Mix for about 3 minutes, or until smooth and creamy.
After your cookies have cooled down, transfer your frosting to a piping bag and frost the top of each cookie. Top each cookie with a light dusting of cocoa powder.
Serve, and enjoy!