Dissolve the yeast in the 1/4 cup of lukewarm milk, making certain that the milk is not too warm. Stir in 1 tablespoon of sugar and set aside. In a deep mixing bowl, combine the butter, remaining sugar, salt and scalded milk, and stir until all are blended. When lukewarm, stir in the yeast. Add the eggs and about 2 cups of the flour, and beat to a smooth batter. Add remaining flour to make a tender dough. Turn out on a floured board and knead for about 2 minutes. Grease a large mixing bowl; grease whole surface of the large ball of dough and place dough in bowl. Cover. Let rise in a warm, not hot, place, to double its bulk. (Takes from 2 to 4 hours.) Again knead on a floured board for about a minute. Roll out 1/8 of an inch thick. Cut into 3to 4-inch circles. Place filling on each. Recipe for Mohn Filling follow. To shape true hamantaschen, pinch eges of a circle together over filling, leaving about 1/2 open, forming a cornucopia. Then fold over the flap and pinch these edges firmly together. Arrange well apart on a greased cookie sheet. Cover with a cloth and let rise again in a wam place to double in bulk. Brush tops with the egg yolk, thinned with a little water. Bake in a moderate oven (350�F) for 15 to 20 minutes. Makes 2 to 2 1/2 dozen.