Separate the egg yolk and keep the white in another small bowl.

Cream together butter, powdered sugar, egg yolk and vanilla sugar.

Add dry ingredients including flour, corn starch and baking powder and mix until the dough comes together with an electric mixer or knead by hand.

Roll the dough into a cylindric shape and cover with some plastic wrap. Rest in the refregerator for 30 mins.

Take out your chilled dough from the refregerator and cut into 0,5 cm discs. Dip the discs in the egg white we kept earlier and then in the crushed hazelnuts.

Bake the cookies in the pre-heated oven set 170C/340F for 13-15 mins. Keep an eye on the cookies and take them out when they get color from the edges.