Put flour, sugar, vanilla sugar, salt, egg and butter in flakes in a mixing bowl. Knead first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Wrap in foil and chill for about 1 hour
Halve the dough and form into a roll (approx. 32 cm long). Whisk the egg yolks with a fork. Spread the rolls with egg yolk and roll them in sugar crystals, press them and refrigerate for about 1 hour.
Then cut each roll into approx. 1 cm thick slices and place on 2 baking trays lined with baking paper. Bake one after the other in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 12 minutes. Remove, place on a cake rack, let cool and pack in tins
waiting time approx. 2 hours