Put 2 cups of the flour in a large mixing bowl. Add 4 of the eggs, one at a time, beating thoroughly into the flour using 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 flour and blend into the dough, breaking up any lumps with either the back of the spoon or your fingers.
Add the starter. 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 9 X 5 X 3-inch loaf pans with the remaining 2 tablespoons butter. To make the rolls, butter 12 standard-size muffin cups.
Punch the dough lightly with your fingers. For loaves, divide the dough into 2 equal portions and place in the pans. For rolls, divide the dough into 12 equal portions and gently drop into the muffin cups. Brush the tops with the egg yolk. Cover and let rise in a warm, draft-free place until it doubles in size, about 1 hour.
Preheat the oven to 400ºF.
Bake the loaves for 25 to 30 minutes and bake for about 20 minutes, or until deep golden brown. Place the pans on a wire rack to cool for several minutes. Turn the loaves and rolls out of the pans and let cool completely on the wire rack.
Slice and serve.
Yield: 2 loaves or 12 brioche rolls