Wipe the meat and remove the skin, bones and gristle. Trim the meat neatly, season well, roll up tightly and tie with string. Slice the onion, celery, carrot and turnip and put into a saucepan with the bones and trimmings, bouquet garni, peppercorns and salt and put the meat on top. Add water to the depth of the vegetables. Cover the meat with greased paper, put on the lid and cook gently for 3 hr., basting occasionally. When the meat is tender, place it between 2 dishes or boards with weights on top, until quite cold. Strain the stock and on the following day boil rapidly until reduced to a glaze. Add colouring if liked. Trim the meat and brush it over with the glaze.