Preheat oven to 325F. Grease a 12-cup mini muffin pan well with butter or coconut oil. In a medium bowl, whisk together the almond flour, erythritol, espresso powder, baking powder, and salt.

In a separate bowl, whisk together the melted butter, egg, and vanilla extract. Pour the wet ingredients into the dry ingredients and stir until well combined. The dough will be thick.

Divide the dough evenly among the 12 muffin cups. Press the dough firmly into the bottom and up the sides of each cup to form a cookie cup. Use a small spoon or your fingers.

Bake for 10-12 minutes, or until the edges are lightly golden and set. Remove from oven and let cool in the pan for 5 minutes before carefully transferring to a wire rack to cool completely.

While the cookie cups cool, prepare the mascarpone filling. In a small bowl, whisk together the room temperature mascarpone cheese and powdered sweetener until smooth and creamy.

Once the cookie cups are completely cool, spoon or pipe the mascarpone filling into each cup. Chill for at least 30 minutes to allow the filling to set.

Just before serving, dust lightly with unsweetened cocoa powder or additional espresso powder for garnish.