Heat oven to 425 degrees F. Degrease stock, and add to a 20-quart stockpot. Bring to a boil, reduce heat, and simmer over medium-low heat. Place chicken in a roasting pan, and roast until skin is golden brown, about 30 minutes. Add short ribs, brisket, bouquet garni, and roasted chicken to stockpot, and simmer for 2 hours.
Reduce oven to 375 degrees F Rub the cut side of the marrow bones with salt. Wash and clean the leeks. Remove the dark green tops, and slice into 20 (1/2 by 9-inch) strips. Cut the whites in 1/2 lengthwise, and set aside. Crisscross 2 strips of leek tops over each marrow bone, and bind with kitchen string. Place marrow bones in a small roasting pan, and add just enough cold water to cover (about 1 1/2 cups). Cover roasting pan with foil, and bake until marrow is opaque, about 1 hour. Remove from oven, keep covered, and set aside.
After the meats have simmered for 2 hours, add celery hearts, reserved leeks, carrots, potatoes, turnips, and cabbage. Cook until vegetables and meats are tender, about 20 minutes. Add the haricots verts, and cook 10 minutes.
To serve, remove meats and vegetables from broth. Serve broth as a first course or as an accompaniment. Slice the brisket against the grain into thin slices. Untie the short ribs, removing any gristle. Separate chicken legs and thighs, and remove breast meat from the bone, slicing into thirds. Place the sliced meats and marrow in the center of a large platter, and surround with vegetables. Pass the garnishes.
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