Begin by whisking together all-purpose flour, granulated sugar, baking powder, and salt in a large mixing bowl. In a separate bowl, cream the unsalted butter until smooth, then add the eggs and espresso powder, blending until fully incorporated. Combine the wet and dry ingredients until a dough forms, then wrap it in plastic wrap and chill in the refrigerator for 30 minutes to firm up.

Preheat your oven to 350°F (175°C) as the dough chills. Once ready, roll the chilled dough into 1-inch balls, ensuring they are smooth and uniform. Pour powdered sugar into a shallow bowl and coat each dough ball thoroughly; this will create the signature crinkle effect. Arrange the coated balls on a parchment-lined baking sheet, leaving ample space between them.

Place the baking sheet in the preheated oven and bake for 10-12 minutes. Monitor closely; they're ready when the edges are lightly golden, while the centers remain soft. As soon as they come out of the oven, create indents in the centers of the cookies using the back of a spoon, making a perfect spot for the filling to go.

While the cookies cool on the baking sheet, prepare the mascarpone filling. In a medium bowl, whip together mascarpone cheese, heavy cream, and an extra dash of espresso powder until the mixture is thick and glossy.

Once the cookies have cooled completely, carefully fill each crater with the espresso mascarpone mixture, using either a piping bag or a small spoon. Be generous with the filling to fully capture the delicious tiramisu essence. After filling, dust each cookie with a light sprinkle of cocoa powder to enhance both flavor and presentation.

For the best texture, chill the filled cookies in the refrigerator for 15-20 minutes if you'd like to set the filling.