The butter mix with powdered sugar. Add egg yolks and flour. Knead the dough and let rest for about 20 minutes. Divide by 2-3 balls which are rolled sheets with a thickness of about 0.5 cm. Cut out circles with a diameter of about 4 cm and rank distance in a slightly greased baking dish with butter. Stir snow egg white with the sugar. Put the mixture with a spoon on the circle and slightly spread. The biscuits are baked in low oven until pale gold color.