Preheat the oven at 180 degrees Celsius.
Let the butter get soft by leaving it in room temperature for about 30 minutes.
Mix the butter with the egg yellows in a bowl with a fork.
Add the sugar, flour and vanilla sugar and mix it all to a smooth dough.
Sprinkle a working bench wit flour and bake approx 2 cm thick square.
Take a round glass or a baking form in preferred size to press out the cookies.
Place the cookies on a baking sheet, and place in the middle of the oven for 10-15 minutes. Let the cookies get slightly brown on the surface.