Put sugar, crumbled yeast, and about 2 tablespoons flour into lukewarm milk; stir well and let it stand in a warm place until it rises. Put flour, a pinch of salt, egg yolks, and melted butter into mixing bowl. Add milk, yeast, and sugar mixture. Beat well with a large wooden spoon for at least 15 minutes. Cover and let it stand in a moderately warm place. After 1 hour, turn out on floured board and pull dough out with fingers until 3/4 inch thick. Can also be rolled on board to 3/4 inch thickness. Cut with glass. Let stand 30 minutes. Heat the fat or oil well. Lower 3 to 4 doughnuts into hot oil and cover. When one side is brown, turn them over - do not cover. When they are browned on both sides, remove, roll in confectioners' sugar, and serve hot. These can also be rolled in cinnamon or regular sugar.