Preheat oven to 400 degrees. Heat a 7 quart or larger dutch oven on low (seriously, you need a pot this big, it makes a ton!) and melt butter.
Transfer Dutch Oven to lower center rack in oven, and cook covered for 1 hour.
Return to oven for 90 minutes with lid slightly ajar. Stir and scrape again half way through. (Onions should be very soft and golden brown.