Cut the tripe into thin strips. Plunge in a large pot of boiling salted water. Boil for 5 minutes then drain and wipe the tripe dry. In a shallow casserole, sweat the thinly sliced onions in the butter and oil. When hot, add the tripe. Cook on a high heat until the excess water has evaporated, then lower the heat and continue cooking without browning. Stir regularly, season with salt and pepper. Towards the end of the cooking, pour the vinegar over the tripe, raise the heat then add the cream. Stir and cook until all the strips of tripe are covered and glazed in cream. Generously sprinkle chopped parsley and serve.
