Mix butter, egg and sugar together.
Add flour and walnuts and knead everything into a dough.
Chill the dough for approx. 1-2 hours.
Then form balls, each about 1.5 – 2 cm in diameter and flatten with a fork. Place on a prepared baking sheet. Bake in a preheated oven at 200°C for about 15 minutes. Roll in sugar or vanilla sugar while still warm.