Put the tripe into a stockpot with two gallons of water, the carrot, parsley, celery, rosemary, onion, bay, and peppercorns. Bring to a boil for one hour and fifteen minutes. Remove the tripe from the pot and allow to cool.
Slice off the ends and spread the tripe out on a cutting board. Slice into strips about a quarter of an inch wide and two inches long.
Strain the stock in which the tripe was boiled and reserve.
Sauce: In a skillet, reduce the milk and cream over medium heat by half. Add fennel seed, demi-glace and tripe stock. Bring to a simmer for about three minutes, then add the sliced tripe.
Simmer tripe in the sauce over medium-low heat for another 10 minutes, or until sauce is good and thick. Add the salt, pepper, and sage, and cook another minute. Serve over fettuccine.