Put the pigs’ feet in a large saucepan and add water to cover. Add the celery, salt, pepper, onion, and carrot. Bring to the boil and simmer 2 hours. Remove the meat from the broth and cool. Reserve ½cup of cooking liquid.
Meanwhile, bake the bread in a 400° oven until it is dried out and browned, but do not let it burn. Grate the bread on an ordinary cheese grater or blend it to make crumbs. Put the crumbs in a sieve and shake them to obtain crumbs of uniform size.
Blend the reserved ½cup of cooking liquid with the mustard and dip the cooled pigs’ feet in it. Coat well and chill.
Preheat the oven to 425 degrees.
Coat the pigs’ feet with bread crumbs. Oil a baking dish and place the pigs’ feet on it. Bake30 minutes. If the pigs’ feet start to burn, reduce oven heat. At the end of 30 minutes, turn pigs’ feet and continue cooking 5 to 10 minutes longer, or until crisp on the outside and tender within. Serve with sauce diable.