Beat the egg yolks, sugar and the butter (must be soft) until melted sugar. Add flour, beating on low mixer. And add vanilla. Leave the dough in the refrigerator for 30 minutes minimum. Frame balls the size of a walnut. Beat the egg whites. I take the ball, put in egg whites, then oval in ground walnuts. Mounted on the baking paper (in the tray from the oven) and leave distance between hedgehogs. Bake in a preheated oven at 180C for 30-40 minutes.