For the cookies, mix the sugar with the vanilla sugar, cinnamon, orangze zest and eggs until creamy. Fold in hazelnuts and refrigerate the dough, covered, for about 30 minutes. If the mixture is too soft after chilling, add some flour.
Preheat the oven to 180°C (approximately 350°F).
Using a teaspoon (dipped in water), scoop small heaps of dough and place on a parchment paper-lined baking sheet. Press a whole hazelnut the center of each. Bake in the oven until golden brown, about 15 minutes. Remove from the oven, decorate with some gold leaf and allow to cool.