Legend has it that bakers started making pastry in the form of crescents following the Turkish siege of Vienna in 1683. Preheat oven to 350. In a large bowl, mix flour, sugar and ground walnuts. Make a little well in the flour mixture and add the egg yolks. Cut butter into small pieces and add to the flour mixture. Knead thoroughly and shape into a ball. Add flour, if needed, to prevent the dough from sticking to the bowl. Cut the ball in 4 parts and shape each part in a roll about inch thick. Cut 1/4-inch pieces and form small crescents in the palm of your hand. Place crescents on a greased baking sheet and bake about 9-10 minutes, until light brown. While still warm, roll the crescents in the confectioners sugar (be careful, they break very easily), then place them on a board to cool. Store in a cookie tin. The flavor actually improves with time. Yield: about 3 dozen.