Preheat the oven to 400 degrees F. Combine the yeast and milk in a small bowl and stir to dissolve the yeast. Add 1 cup flour and mix to blend well. Using a knife, scrape the vanilla bean and stir the pulp into the yeast mixture. Let sit at room temperature in a warm, draft-free place for about 2 hours to allow fermentation. Put 2 cups of the flour into a large mixing bowl. Add 4 of the eggs, one at a time, beating thoroughly into the flour sing a wooden spoon with each addition The dough will be sticky, thick, and spongy. Add the water, sugar, and salt and mix well, beating vigorously. Add 3 sticks of the butter and work it into the dough with your hands until it is well blended Add the remaining 2 eggs and mix well into the dough. Add the remaining 2 cups of flour and blend into the dough, breaking up any lumps with your fingers. Add the yeast mixture. Using your hands, knead and fold the starter into the dough Continue kneading and folding until all is well mixed, about 5 minutes. The dough will be sticky and moist. Cover with a clean cloth and let rise in a warm, draft-free place until it doubles in size, about 2 hours. To make loaves, lightly butter two 9x5x3 inch loaf pans with the remaining 2 tablespoons butter. To make rolls, butter 12 standard-size muffin cups. With your fingers, lightly punch down the dough. Divide the dough into 2 equal portions and place in the pans. For rolls, divide the dough into 12 equal portions and place in the muffin cups. Brush the tops with egg yolk. Cover and let rise in a warm, draft-free place until it doubles in size, about 1 hour. Bake the loaves for 25 to 30 minutes and the rolls for 20 minutes, or until golden brown. Remove the pans from the oven and cool on wire racks. Turn the loaves or rolls out of the pans and cool completely on the wire rack.