1. In a heavy 3- to 4-quart saucepan or flameproof casserole that has a cover, heat the olive oil until a light haze forms over it.
2. Add the onions and celery and cook over moderate heat for 8 to 10 minutes, stirring frequently, until the onions are soft and slightly golden.
3. Add the tripe and toss it with the onions and celery until they are well combined.
4. Dissolve the tomato paste in the stock and pour it over the tripe and vegetables.
5. Add the parsley, garlic, marjoram and salt. Bring to a boil over high heat, then reduce the heat, cover the pan and simmer the tripe slowly, regulating the heat so that the surface of the sauce barely moves.
6. If at any point the sauce becomes too thick, add a few tablespoons of stock. In 2½ to 3 hours, the tripe should be tender when pierced with the tip of a sharp knife.
7. Serve as hot as possible on heated plates. Sprinkle each serving with grated cheese.
