Meanwhile, while the tripe is cooking, make your tomato sauce: In a pot, crisp up the guanciale or pancetta until brown and crispy and the fat renders out. If not using, heat up 1-2 tablespoons of oil over medium heat. Add the onion and garlic and cook, until soft but not brown. Stir in the crushed red peppers and tomato paste. Add the tomatoes, the cut up tripe, and 1/2 cup of the tripe cooking liquid. Bring to a simmer for for 30 mins to 1 hour, partially covered. Taste, season, and finish generously with parm. Enjoy with toasted bread, if desired.