In a large mixing bowl, whisk together all-purpose flour, granulated sugar, baking powder, and salt until well combined. In a separate bowl, cream unsalted butter until smooth and fluffy. Add in the eggs and espresso powder, mixing until thoroughly incorporated. Cover the dough and chill it in the refrigerator for 30 minutes.

Preheat your oven to 350°F (175°C). After chilling, scoop the dough and roll it into 1-inch balls. Coat each ball in powdered sugar and place them on a parchment-lined baking sheet.

Slide the baking sheet into your preheated oven and bake for 10-12 minutes until lightly golden around the edges and soft in the center.

Use the back of a spoon to gently press down in the center of each cookie while still warm, forming a small indent.

In a medium mixing bowl, whip together the mascarpone cheese and heavy cream using an electric mixer on high speed until thick and glossy, about 2-3 minutes.

Once the cookies have cooled, fill each indent with the prepared espresso mascarpone mixture. Dust the tops lightly with cocoa powder.

For the best flavor and texture, refrigerate the filled cookies for 15-20 minutes before serving.