Heat the oven to 120°C.
Mix the ground hazelnuts, cinnamon, cloves and lemon zest in a bowl.
In another bowl, whisk the egg whites and vanilla essence until stiff peaks form, then gently sift in the icing sugar and combine. Set aside 4 Tbsp of the foam, then add the rest to the hazelnut mixture. Mix well until you get a pliable dough.
Roll the dough out between two sheets of baking paper to a thickness of 5mm. Remove the top baking paper and stamp out star shapes, using a cookie cutter.
Transfer the cookies to a baking sheet lined with parchments paper and brush on the reserved egg white in a thin layer. Bake for 15 minutes on the lower shelf in your oven (otherwise the egg white might burn).
Lower the oven temperature to 100°C and bake for another 15-20 minutes until the cookies are cooked through.
Let the cookies cool on a wire rack, then store them in an airtight container.