Preheat the oven to 180°C. Prepare as many baking sheets as you can to be quick with the baking process.
In a food processor, chop walnuts finely. They should have the consistency of rough flour.
In a bowl mix flour, icing sugar, walnuts, butter and egg yolk using your hands and fingers. Make a soft and silky dough. Let rest for 15 minutes in the fridge.
Take the dough out of the fridge and put it on a floured surface. Cut the dough into more parts. Roll every part of the dough into a strand about 2 cm thick. Cut the strand into 10 cm parts. Roll each piece into a shape of a crescent and put it on the baking sheet.
Bake for 10-12 minutes until there is a little golden colour. Let them cool for 2-3 minutes and then cover with icing sugar and vanilla sugar in another bowl. Be careful so they don't break!
