Trim the pork and lamb and cut into bite-size pieces; season with salvt and pepper and reserve.
Sort and rinse the beans. Place them in a pot and add enough chicken stock to cover them by about 2 inches. Bring the stock to a simmer and cook the beans over low heat for 30 minutes. Add the bacon and continue to simmer for about another 30 minutes. Add the garlic sausage, halved onion, and bouquet garni and continue to simmer until the beans are very tender and creamy, about another hour. Remove and discard the sachet and halved onion. Hold the beans in their cooking liquid. Remove and reserve the bacon and sausage.
Heat oil in a large pot until it starts to shimmer. Place the pork and lamb carefully in the oil to sear a deep brown on all sides. Remove to another pan and reserve the meat with their juices.
Add the diced onoins, celery and garlic to the pot and cook until limp and translucent, about 5 minutes. Add the wine and stir to deglaze the pan. Add the tomatoes and cook until the juices released by the tomatoes have cooked down, about 5 minutes.
Return the lamb and pork to the pot along with their juices. Add enough brown beef stock to barely cover the meat and return the stew to a slow simmer. Add the sachet, cover the pot, and transfer it to a 350° oven and stew until the meat is tender, about 1 1/2 hours. Stir the stew from time to time and add more stock if necessary to keep the meat moist.
Pull the meat from the duck legs, remove the skin, and pull or shred into bite size pieces. Remove the rind from the bacon and chop into bite size pieces. Peel the sausage and slice thin.
Arrange the duck, stew meat, bacon and sausage in a casserole or other baking dish. Add the beans and some of their cooking liquid. Add some of the stewing liquid from the meats. The cassoulet should be very moist but not soupy. Top with a layer of breadcrumbs and bake in a 350° oven for about 20 minutes or until the breadcrumbs are golden brown and bubbling around the edges. Sprinkle with chopped parsley and serve.
Season duck legs liberally with salt and let them cure under refrigeration for 24 hours. Rinse the salt from the legs. Using the fat from the skin, render enough fat to completely submerge the duck legs (melt shortening if there is not enough fat from the skin). Poach the duck in the fat until it reaches an internal temperature of 170° (about 1 hour). Remove from the oven and cool and store the duck covered in the fat. Scrape and rinse the excess fat before using.