Bring 5 quarts of water to a boil in a large pot.

Add 2 pounds of dry white beans to the boiling water and boil for 2 minutes.

Remove from heat and let the beans soak in the warm water for 1 hour.

Place 1/2 pound of slab bacon, one third of the diced onions, and the bouquet garni bundle in the pot with the beans.

Bring to a simmer and skim off any scum that rises to the surface.

Simmer, uncovered, for about 1 1/2 hours, or until beans are just tender, adding water as needed.

Drain the beans, reserving the cooking liquid. Save the bacon and discard the herb bundle.

Cut 1 pound of boned shoulder of lamb into 2-inch chunks, removing excess fat and patting dry.

Pour 2 tablespoons of duck fat into a heavy, 8-quart casserole and heat until almost smoking.

Brown the lamb in batches on all sides and set aside.

Lower the heat and add the remaining diced onions. Sauté until golden, about 3 to 5 minutes.

Add 2 tablespoons of pureed garlic, 1/3 cup of tomato puree, 1 teaspoon of dried thyme, and 2 bay leaves.

Cook for an additional 2 to 3 minutes.

Add 3 cups of dry white wine and reduce by half.

Return the lamb to the casserole along with 1 quart of brown duck stock, salt, and pepper. Stir well.

Bring to a simmer, cover, and simmer slowly for 1 to 1 1/2 hours, or until lamb is fork tender.

Remove the lamb and reserve.

Remove all but 2 tablespoons of 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 heat and let stand for 10 minutes.

Drain the beans, reserving the cooking juices.

Preheat the oven to 375 degrees F (190 degrees C).

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 confit (cut into 2-inch pieces), 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 2 cups of dry bread crumbs with 1/2 cup of finely chopped parsley and spread over the top.

Drizzle with 4 tablespoons of melted 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, turn the oven down to 350 degrees F (175 degrees C).

Break the crust with a spoon and baste the casserole with the liquid.

Bake for about 40 more minutes, continuing to baste as the crust reforms, but leave a final crust for serving.

Serve warm from the casserole.