Grind the 12-15 cups of flour and set aside. (Or do the 1/2 and 1/2 mixture)
Then add 3 tbsp. salt to mixture. Do not forget this!
Add enough remaining flour to create a soft and slightly moist dough, one cup at a time. Knead in mixer 5-7 minutes or until gluten is fully developed. Then cover and let rise until double and punch down before shaping.