Preheat your oven to 350°F (175°C) and prepare a muffin tin by greasing it lightly or using cupcake liners.
In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
In a large bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy.
Add the egg and vanilla extract, mixing until fully combined.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Scoop the dough into the prepared muffin tin, pressing it into the bottom and up the sides to create cup shapes.
Bake for 10-12 minutes or until the edges are lightly golden and the centers look set.
Remove from the oven and let cool in the tin for a few minutes before transferring to a wire rack to cool completely.
In a separate bowl, beat the heavy cream with powdered sugar until stiff peaks form.
Fold in the mascarpone cheese until smooth and creamy.
Soak each cookie cup with the cooled espresso, allowing a bit to soak in without making them soggy.
Pipe or spoon the mascarpone filling into each cookie cup, smoothing the top as desired.
Lightly dust with cocoa powder before serving to add a touch of elegance.