Cut the butter into pieces. Knead the sugar, butter, flour, vanilla sugar and egg first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Wrap the dough in foil and chill for about 30 minutes. Divide the dough into three. Knead 1/3 with cocoa.
Roll out all the dough pieces on a floured work surface to form a rectangle (7 x 15 cm) and place on top of each other. Wrap in cling film and chill for approx. 30 minutes. Cut the dough into sticks of approx. 20 approx. 7 cm in length and place them on a baking tray lined with baking paper. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 8 minutes. Let the biscuits cool down on a cake rack
waiting time approx. 1 1/2 hours