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 45 minutes. Whisk egg yolk and milk. Form cherry-sized balls from the dough with your hands. Place on 3 baking trays lined with baking paper.
Press a depression in the middle of each ball with a finger. Fill the hollows with jelly. Brush the edge of the dough with egg yolk. Bake one after the other in a preheated oven (electric: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 12 minutes. Remove from the oven, place on a cake rack and let cool off. Pack in tins
Waiting time 1 hour