Dissolve yeast in lukewarm water. Stir to dissolve. Add yeast mixture to flour in small bowl. Stir with spoon until it forms a stiff ball. Turn out on lightly floured board. Knead a little until you get a smooth surface on top. Cup dough in your hands to make round top and cut halfway through ball with sharp knife in the shape of an "X" like a hot cross bun. Open each of four petals a little. Drop it into a 4 cup pitcher half filled with lukewarm water and leave it to rise to the top of the water. This will happen in 3 to 7 minutes. In the meantime in large mixing bowl beat the butter until light and fluffy. Remove butter with rubber scraper, cleaning bowl thoroughly with scraper. Place butter aside. In mixer, place flour, sugar, salt and eggs. Beat until shiny. Add butter and well-drained yeast dough. Mix all together with spoon and put in floured bowl. Cover dough with saran wrap and cloth and put into warm place to rise, until double in bulk -3/4 to 1 hour. When risen, stir around top with finger to break the rise. Cover and put in the refrigerator overnight or in the freezer 2 to 3 hours. Remove dough and work quickly so it won't get too sticky to handle. Place on floured board. Shape two-thirds of dough into balls-the size will depend on the size of the muffin tins you use. Regular 3 inch tins take 2 inch balls. Miniature muffin tins take 1/2 inch to 3/4 inch balls. Place the balls in well-buttered muffin tins.
Form an equal number of small balls from remaining third of dough. Shape one end into cone shape. With finger make depression in center of large ball and insert tip of cone. Press gently. Cover loosely with towel and let rise in warm place until double in bulk, about 1 hour. Brush lightly with mixture of egg yolk and milk.
Bake at 425 for 15 to 20 minutes for large brioches and 10 to 12 minutes for miniatures. Cool quickly and freeze. To serve, remove from freezer and heat at 300 until thawed and heated through.