Beat the butter with powdered sugar until light and fluffy - I beat for about 3 minutes on the highest speed of the mixer.

Add the egg to the butter and mix briefly on low speed.

Add part of the flour to the eggs and mix on low speed until just combined.

Add baking powder and salt - mix briefly.

Add instant coffee powder and mix briefly.

Add the rest of the flour and mix briefly - just until combined.

Place the bowl with the dough in the refrigerator for about 30 minutes - so that the mixture slightly firms up.

Preheat the oven to 180 ℃ (conventional) or 170 ℃ (convection).

Scoop portions of dough with a large spoon.

Roll balls in your hands the size of a large walnut.

Arrange the cookies spaced apart on a large baking sheet lined with parchment paper.

Bake the cookies in a preheated oven for about 14 minutes.

After baking, the cookies will still be very soft; they will start to harden slightly after cooling.

Transfer mascarpone, heavy cream, and powdered sugar to a bowl.

Blend them into a thick cream.

Apply the cream to the cookies - you can transfer it to a piping bag and cut off a corner to make the cream look nicer.

Finally, sprinkle the top of the cookies with bitter cocoa.