Mix the butter and sugar together in a food processor till soft, then add the egg and pulse for 10 seconds. Add the baking powder, cocoa powder and flour and pulse to form a soft pastry. Remove the pastry, and chill for 30 minutes in the fridge to firm up. Next, form the chilled pastry into small balls, and flatten them down. Mix the chopped hazelnuts and chocolate chips together in a large plate and dip in the flattened pastry balls, pressing down well, to coat the cookies with chocolate chips and nuts. Place the cookies on lined baking sheets, slightly apart, and bake in the oven at 200`c for about 15 minutes. When cooked, remove the chocolate and hazelnut cookies from the oven and leave to cool on a wire rack.