Mound flour on the work surface with sugar, vanilla sugar and lemon zest. Make a well in the center, add the egg to the well and top the flour with butter in small pieces.
Mix everything together by chopping with a large knife to crumbs.
Knead crumbs with hands quickly. Wrap in foil and refrigerate for about 30 minutes.
Press dough until slightly flat on a floured surface and roll out to about 3 to 4 mm (approximately 1/8-1/4 inch) thickness.
Loosen from work surface with a spatula.
With a star-shaped cookie cutter, cut out cookies and put on a parchment paper-lined baking sheet. Place in preheated oven at 180°C (approximately 350°F) convection and bake until golden brown, 10-12 minutes.
While still hot, transfer cookies with a spatula to a wire rack and sprinkle with vanilla sugar. Let cool before serving.