Put the beans in a large pot and cover with cold water by 6 inches , soak overnight and then drain.
season pork belly cubes with 1 tablespoons of the salt and 2 tsp of the pepper . Heat large pot preferably cast iron, over med- high heat.
heat oven to 250 degrees.
sear the belly pieces in the rendered belly fat until lightly browned about 2-3 minutes . add the onion celery carrots garlic bay leaves red pepper flakes, and thyme plus the remaining 1 tsp salt and 1 tsp pepper.
sauté until the vegetables start to soften, about 5 minutes pour in the wine and simmer to slightly reduce about 3 minutes add the tomato paste and mustard and cook, stirring until the ingredients are combined.
return the seared pork belly and its juices to the pot. add 1 qt of the chicken broth and bring to a simmer. then cover. and simmer for 60-70 minutes the pork belly will be cooked and slightly tender but should not fall apart.
add the beans and remaining 1 qt broth, or enough to comfortably cover the beans by 2 inches. put in the oven and bake , uncovered, stirring the top crust into the beans every hour or so, until the beans are tender. about 3 1/2 hours. add a little more broth if needed to keep beans moist and submerged.
Increase the oven temp to 450 cook for another 30 mins to form a crust on top of the bean mixture. push the crust to the middle of the pot. cook for another 15 mins to form a new crust. The cassoulet will have a deep brown crust and look rich. Cool for at least 30 mins before serving.