Oven heated to 160 C. Forms for small cookies covered with baking paper. In a large bowl mix the butter and sugar, beating gently and at the same time add the yolks. Mixing until a creamy mixture. Add the liqueur and orange and lemon peels. Finally, add the flour and a pinch of salt and stir everything nice. Pour the mixture carefully into trays of sweets. Top add a little whipped snow white and walnuts. All sprinkled with sugar and put in the oven for 25 minutes. The cookies should stay there until browned nicely. Turning off the oven, open the door, but leave the cookies inside for another 15 minutes.