A bison shank, Osso Buco when portioned, is a rather large bone that has to be cut up so that it fits into a pan. The meat is lean, has very little fat, and is extremely tender. The gold in the Osso Buco is the marrow found in the shank bone. This is a slow-cooking dish and well worth the wait. Make sure you fish out the bone marrow from the bone before you finish the dish.