Mix flour, starch, sugar, salt and baking powder in a bowl. Press a depression in the middle, add butter, milk and 3-4 tablespoons beetroot juice and knead quickly with your hands (use disposable gloves if necessary) to a smooth dough. Finally, knead in the chocolate flakes.
Form the dough into a roll of approx. 4 cm thickness/ approx. 38 cm long, wrap in foil and chill for approx. 1 hour. Cut the roll into 6-7 cm thick slices and place them on 2-3 baking trays (32 x 40 cm) lined with baking paper. Bake one after the other in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 10 minutes until the edges of the thalers begin to brown slightly.
Let the finished cookies cool on a cake rack. Mix icing sugar and 2 tablespoons beetroot juice to a smooth glaze. Put the icing in a disposable piping bag and cut off a small tip. Spray the icing in strips onto the cookies and leave to dry.