The pork for this crowd pleaser can be roasted a day ahead, shredded and chilled. Slideshow: More Cajun and Creole Recipes
Preheat the oven to 350°F. Place the pork butt in a roasting pan and season all over with 2 teaspoons salt and 1 teaspoon pepper. Place 1 cup of the water in the pan and cover tightly with foil. Roast the pork until very tender, about 4 hours. Let cool to warm then shred pork with a fork, reserving cooking liquid. Skin fat from cooking liquid, reserving 2 tablespoons of fat.
In a large heavy pot, heat the reserved fat over medium high heat until hot. Add the sausage to the pot and cook, turning once, until golden brown, about 6 minutes. Transfer the sausage to a bowl. Stir the onions, belly peppers, celery, 1 teaspoon salt and 1/2 teaspoon pepper into the pot. Cook vegetables, stirring occasionally, until translucent, about 8 minutes. Stir in the garlic, bay leaves and cayenne and continue to cook until golden, about 6 minutes. Stir in the tomatoes, rice, remaining 3 cups water reserved pork butt and reserved sausage and bring to a boil. Reduce heat to a simmer and cook until the rice is tender, about 20 minutes. Season the jambalaya with salt and pepper to taste, then sprinkle with the parsley and serve.