In a 10- to 12- quart saucepan or stockpot, combine the beef, marrow bones, knuckle, and beef stock. The stock should cover the meat by about 4 inches; and more stock or water if needed. Bring the stock to a boil over moderate heat while skimming off the scum that rises to the surface.
Meanwhile, melt 2 tablespoons of butter in a heavy 6- to 8- inch skillet, and cook the whole onions and halved carrots over moderate heat, turning them often, until they are lightly browned.
When the stock comes to a boil, reduce the heat to low, and add the browned onions and carrots, chopped tomato, bouquet garni, thyme, peppercorns, and salt. Partially cover the pot and simmer slowly, undisturbed, for two and a half hours, until the beef is almost tender when pierced with the tip of a sharp knife.
Transfer the beef to a plate. Remove the bones from the stock, and scoop out their marrow with the point of a knife before discarding them. Set the marrow aside in a bowl.
Strain the stock into a bowl through a fine sieve lined with a double layer of dampened cheesecloth. Discard the vegetables and skim the surface fat from the stock. Wash and dry the pot, then return the stock and meat to the pot, and add the garnish of carrots, turnips, parsnips, and the leeks. Bring the stock to a boil and simmer, uncovered, over low heat for 30 minutes, or until the meat and vegetables are tender. If the vegetables cook faster than the meat, remove them from the pot and cook the meat until it is tender; then return the vegetables to the pot and heat them through.
Blanch the cabbage by plunging it into boiling salted water and cooking it over high heat for eight minutes. Drain the cabbage and add it to the meat and vegetables in the pot after they have cooked for 20 minutes. Boil the potatoes separately.
When the meat and vegetables are done transfer the meat to a carving board, remove the strings, and carve the roast into ¼-inch slices. Arrange the slices attractively, overlapping slightly, on a heated platter, surrounded by the vegetables and potatoes, cover the platter loosely with foil, and set aside. With a spoon, skim as much fat as possible from the surface of the stock. Chop the marrow into fine dice and add it to the pot. Serve the stock, sprinkled with chopped fresh parsley, as a first course, then present the meat and vegetables.
Serving Size 6-8 people