Step 1Sort through the beans to remove any stones. Cover by 3 inches with cold water and soak overnight.
Step 2Combine the duck fat and whole garlic cloves in a very small baking dish. Bake at 300 degrees for 30 minutes, until the garlic is very soft. Strain the fat and reserve; set the garlic aside.
Step 3Heat 2 tablespoons of the duck fat from the garlic in a Dutch oven or a deep, heavy soup pot over medium heat. Add the pancetta or bacon, chopped garlic, onions and celery and cook until the vegetables are tender, about 5 minutes.
Step 4Drain the beans and add to the pot, stirring to coat with fat. Add 2 quarts of water and bring to a boil. Reduce to a simmer, cover and cook 40 to 50 minutes, until the beans are turning tender.
Step 5Meanwhile, bring a large pot of water to a rolling boil. Cut the trimmed cabbage into 6 wedges and blanch 5 minutes. Remove and drain very well. Cut crosswise into 1-inch strips, discarding the thickest ribs of the heaviest leaves. Heat 3 tablespoons of the garlic duck fat in a large, deep skillet and add half the cabbage, turning to coat all sides. Cook 3 to 4 minutes, until the cabbage is softened and just beginning to take on color. Transfer to the soup pot. Repeat with the remaining duck fat and cabbage and add to the pot.
Step 6Add the duck legs and carrots to the pot. Cover and cook about 40 minutes, stirring occasionally, until the vegetables are very tender. Season with 2 teaspoons salt and pepper.
Step 7Remove the pancetta or bacon and duck legs from the soup and place on a cutting board. When it's cool enough to handle, cut the pancetta or bacon into 1-inch pieces, discarding the extraneous fat. Return the meat pieces to the soup pot. Remove and discard the skin from the duck legs and roughly shred the meat into large chunks. Return the duck meat to the soup and add the garlic cooked in duck fat. Simmer, covered, for 10 minutes. Taste and add more salt if needed and lots of black pepper.
Step 8If not serving immediately, cool slightly, then refrigerate until cold. Scrape off and discard any fat congealed on surface before reheating.
Step 9To serve, ladle into bowls, making sure meat and other ingredients are evenly divided. Serve plain or ladled over a thick slice of sturdy bread. Makes 14 cups.