Dissolve coffee powder in 1 teaspoon of hot water. Grate the chocolate. Mix butter, brown sugar, egg and coffee. Stir in flour, nuts, baking powder and chocolate. Fill dough into a piping bag with perforated spout. Pour into small paper sleeves or heat-resistant espresso cups.
Beat the egg whites until stiff, allow white sugar to trickle in. Spread over the cookies. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 15 minutes. Cover if necessary. Leave to cool and dust with a little cocoa