Mix flour, baking powder and cocoa in a bowl. Cream butter, sugar and brown sugar. Stir in egg. Add flour mixture and stir in as well. Chop 100 g chocolate and stir into the dough.
Spread the dough on a piece of foil to form a flat plate. Wrap in foil and chill for about 30 minutes.
Divide the dough into about 20 portions and form them into balls. Press each ball into a flat taler, place the taler on 2 baking trays lined with baking paper. Place a nut in the middle of each taler.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 12 minutes one after the other. Allow to rest briefly on the tray, then carefully place on a cake rack and allow to cool.
In the meantime, chop the remaining chocolate and melt it over a hot water bath. Pour into a piping bag with a fine perforated nozzle. Spray fine strips onto the cookies. Let the chocolate dry. Arrange the cookies on a plate and decorate with raspberries if desired.