Preheat the oven to 350°F (175°C).
In a mixing bowl, whisk together the flour, baking powder, and salt.
In another bowl, cream the softened butter and granulated sugar together until light and fluffy.
Add the egg and vanilla extract to the creamed mixture, mixing until fully incorporated.
Gradually add the dry ingredients to the wet mixture, blending until just combined.
Grease a muffin tin and scoop the dough into each cup, pressing down lightly to form a cup shape.
Bake for 10-12 minutes, until the edges are golden brown.
Remove from the oven and allow the cookie cups to cool in the pan for 5 minutes before transferring them to a wire rack.
In a separate bowl, whip the heavy cream until stiff peaks form, then fold in the mascarpone and cooled espresso.
Fill each cooled cookie cup with the mascarpone mixture and top with cocoa powder and chocolate shavings.
Chill the completed cookie cups in the refrigerator for at least 30 minutes before serving.