Dissolve yeast and sugar in 1 cup warm water. Proof 5 minutes (to activate yeast).
Combine 8 cups flour with 2 teaspoons salt in mixture bowl. Using paddle attachment, mix in the yeast mixture and remaining 4 cups water.
Switch to dough hook and mix 10 minutes, adding in remaining flour as needed until dough is smooth and elastic.**
Place dough in a well-oiled bowl. Cover with plastic and let rise until doubled in bulk, 45 minutes for 1 hour.
Meanwhile, slice onions thinly and sauté in ¼ cup oil in large pan over medium heat until golden brown, 10-15 minutes. Season with pepper, Rosemary, and remaining 2 teaspoons salt. Set aside.
Punch down dough and spread onto an oiled full sheet pan; let rise 10 minutes.
Dimple dough with fingertips and brush with remaining ¾ cup Olive oil. Bake at 425°F for 10 minutes.
Remove from oven and top with onion mixture. Sprinkle with Parmesan and bake 10-15 minutes longer, or until golden brown. Cool slightly and cut into serving size pieces.