Mix flour and baking powder. Add the butter in flakes, 1 egg, sugar and vanilla sugar and quickly work into a smooth dough with the dough hooks of the hand mixer. Halve the dough. Knead cocoa, cappuccino powder and milk under one half of the dough. Wrap doughs in foil and chill for 30 minutes. Roll out both doughs into a rectangle (25x20 cm) on a floured work surface. Brush light-coloured plate with egg white.
Place dark plate on top. Roll up the plates from the long side, wrap in foil and chill for 1 hour. Cut the roll into 30 slices. Place on 2 baking trays lined with baking paper. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: 3) 10-12 minutes in a row. Remove cookies from the oven and let them cool down on a cake rack. Store cookies in a cookie tin
waiting time approx. 1 1/2 hours