Set a large cast iron skillet or Dutch oven over high heat. Cook the sausage until browned on all sides. Remove to a plate. Brown the pork in the sausage fat, making sure not to crowd the pan, in batches until browned on all sides. Set aside on a plate with the sausage. Next, brown the chicken pieces until the skin is golden brown. Set aside.
Place the onion, carrots, celery, and tomatoes in the bottom of the slow cooker, followed by the white beans, pork, chicken and sausage, in that order. Pour the wine and stock over the meat. Submerge the bay leaves and thyme in the mixture. Cook on low heat for 8 hours, until the meat is falling off the bone and the liquid has reduced.
For the stove-top: Add the onion, carrots, celery, and to the Dutch oven, followed by the white beans, pork, chicken and sausage, in that order. Pour the wine and stock over the meat. Submerge the bay leaves and thyme in the mixture. Cook uncovered in a 300 degree oven, until the meat is falling off the bone and the liquid has reduced, about 2 hours.
Serve the cassoulet family-style with crusty baguette.