Put the flour in the bowl and sprinkle with the sugar and vanilla sugar. Make a well in the middle and put the butter in flakes on the edge. Put the yolks and egg in the well, add the lemon zest and salt and quickly knead everything into a smooth dough with the dough hook or your hands. Chill the dough in a closed bowl for at least an hour.
Roll out the dough on a floured surface and cut out shapes (e.g. stars or hearts). Place on a baking sheet with baking paper. Brush with egg yolk and decorate to taste. Bake at 175 ° C for 10 - 12 minutes.