In Italy, you can find tripe that has been almost entirely pre-cooked, so that you need only simmer it with the tomato sauce for, say, 30-45 minutes and it’s ready to eat. Outside Italy, you can sometimes find pre-cooked tripe in Italian neighborhoods. Otherwise, tripe does usually come partially pre-cooked, but still needs considerable further cooking before you can use it for this dish. Pre-cooking also removes some of the ‘gamy’ flavor that tripe can sometimes have. Simmer the whole tripe in water to cover with an onion, garlic and a spring of parsley (you can add carrot and celery, too, if you like) for about an hour. Or more: some tripe you buy can take as long as 3 hours to cook, so ask your butcher or store assistant about it.