For the ponce, prepare a smoker with hickory wood and bring to 175ºF by following the equipment directions.Place the pig’s stomach in a colander and rinse thoroughly under cold water. In a large bowl, mix the water and salt. Submerge the stomach in the saltwater solution and place in the refrigerator for 30 minutes. Remove and inspect the stomach to make sure that it is clean, being careful not to tear the delicate tissue. Place on paper towels and let dry. Refrigerate until ready to stuff.In a large skillet over medium-high heat, add 2 tablespoons of oil. Once the oil is hot, add the onion, celery, and bell pepper and cook until the onions become translucent, about 5 minutes. Add the garlic and thyme and cook for 1 minute more. Remove the skillet from the heat and pour the contents into a large mixing bowl. Add the sweet potatoes and pork and season with Cajun seasoning and pepper. Combine making sure the ingredients are distributed evenly.Move the pig’s stomach to a large cutting board and open it up. Using your hands, gently stuff the meat mixture inside the stomach. Add just enough filling so that the lining of the stomach can come together and seal. Using butchers twine, sew the stomach closed. (Note: Alternatively, some use toothpicks to close the stomach.)Place the stuffed ponce on a rack in the smoker. Smoke for 4 hours at 175ºF. Once smoked, remove the ponce.Preheat the oven to 350ºF.In a heavy cast iron pot with a tight-fitting lid, add the smoked ponce. Place the carrots, onions, and celery in the pot and add enough chicken stock to come halfway up the side of the stuffed ponce. Add 2 tablespoons of dark roux. Cover the pot and place in the oven for 2 hours. Once the ponce has finished roasting, remove it to a platter and keep warm.Pour the gravy and vegetables through a strainer and into a saucepan. Over high heat, bring the stock to a simmer and skim off any fat or particles. Let reduce on a simmer for 5 minutes. Turn off the heat and keep warm.For serving, move the stuffed ponce to a cutting board and slice into ½-inch-thick slices. Place on a platter family-style and serve with white rice and plenty of gravy on the side.