Fill a large pot with the water and bring to a boil. Add the beans, bring back to a boil and boil for 2 minutes. Remove from the heat and let the beans soak in the warm water for 1 hour.
Place the slab of bacon, one third of the onions, and the bouquet garni bundle in the pot with the beans and bring to a simmer, skimming off any scum that rises to the surface. Simmer, uncovered, for about 1 1/2 hours, or until beans are just tender, adding water if necessary to keep the beans covered while cooking. Drain the beans, reserving the cooking liquid, saving the bacon, and discarding the herb bundle.
Cut the lamb into 2 inch chunks, removing excess fat, and pat dry. Pour the duck fat into a heavy, 8 quart casserole, and heat until almost smoking. Brown the meat, in batches, on all sides, and set aside. Lower the heat, add the remaining onions, and saute until golden, about 3 to 5 minutes. Add the pureed garlic, tomato puree, thyme, and bay leaves, and cook an additional 2 to 3 minutes. Add white wine and reduce by half.
Return the lamb to the casserole along with the brown stock, salt and pepper, and stir well. Bring to a simmer, cover, and simmer slowly for 1 to 1 1/2 hours, or until fork tender.
Remove the meat and reserve. Remove all but 2 tablespoons fat and adjust the seasonings.
Pour the cooked beans into the lamb cooking juices. If necessary, add the bean cooking liquid so that the beans are well covered. Bring to a simmer, cook for 5 minutes, then remove from the heat and let stand for 10 minutes. Drain the beans, reserving the cooking juices.
Preheat the oven to 375 degrees F.
Slice the bacon into 1/4 inch pieces. Arrange a layer of beans in the bottom of the casserole, then continue with alternating layers of lamb, and duck, ending with a layer of beans. Pour enough of the meat and bean cooking juices over the top so the liquid comes just to the top layer of beans. Mix the bread crumbs with the parsley and spread over the top. Drizzle with the duck fat.
Bring the casserole to a simmer on the stove, then place it in the oven. After about 20 minutes, when the top has a light crust on it, turn the oven down to 350 degrees F. Break the crust with a spoon and baste the casserole with the liquid. Bake for about 40 more minutes, and continue to baste as the crust reforms, but leave a final crust for serving. Serve warm from the casserole.
c.1997, M.S. Milliken & S. Feniger, all rights reserved