Peel and thickly slice the yellow, red, and sweet onions. Put about 1/2 into the big La Crusset pot with all the fats. Turn heat up to high, and watch till onions wilt enough to add the remaining onions.... can add in batches. When all the onions are in the pot, add the remaining ingredients, and continue to cook and stir for a few hours over medium heat. Idea is to reduce down some of the liquids that accumulate.
Place in 200 oven for up to 24 hours. Remove when onions are nice and brown.