Place the flour, cold cubed butter, sugar, vanilla sugar, a pinch of salt, and egg in the food processor. Process shortly to form the dough.

Turn the dough onto the working surface and press the dough into a disc. Wrap in plastic foil and refrigerate for 30 minutes or longer.

Preheat the oven to 350°F (180°C) and line the baking trays with parchment paper.

Roll the dough about 0.2 inches (5 mm) on a lightly floured surface with a lightly floured rolling pin. Cut the cookies with any cutters you like and place on trays.

Mix the egg yolk and the milk, brush the cookies with the mixture, and sprinkle with sprinkles.

Bake for 7-10 minutes until only lightly golden. Let rest on the tray for 5 minutes, then transfer to wire racks to cool completely.

Roll the remaining dough and repeat the process with scraps.