The night before, cover beans in 1 L water with 3 tablespoons salt and let sit at room temperature overnight.
The day of, drain beans and set them aside, and if using gelatin, sprinkle it into the chicken stock. Dice onion, peel garlic, and roughly chop carrot and celery.
Heat duck fat (if using it) in a large Dutch oven until very hot, then add salt pork and brown it. Set meat aside in a bowl when cooked.
Repeat the above with garlic sausage.
Season chicken pieces with pepper (no salt) and repeat the above.
Drain all but 2 tablespoons fat from pot and cook onions in fat until translucent.
Add vegetables and spices (omit meat), and simmer until beans are al dente, about 45 minutes.
Remove carrots, celery, parsley, bay leaves, and cloves and discard.
Stir pork and sausage into pot and set chicken pieces on top beans with skin facing up.
Transfer pot to oven and cook at 300°F, uncovered. Gently add water/stock as necessary to keep beans mostly covered.
At the 2-hour mark, break crust with a spoon and agitate pot gently side to side, then return it to oven and continue cooking until crust is deep brown and thick, about 5 to 6 hours total. Keep adding water as needed to keep beans from drying out.