Spread the beef shanks, the veal shanks, the onions, and the carrot in a flameproof baking pan, brown them well in a preheated 450° F. oven, and transfer them to a kettle. Add 2 cups water to the pan, deglaze the pan over high heat, scraping up the brown bits, and add the liquid to the kettle with 14 cups cold water, the celery, the salt, and the cheesecloth bag. Bring the water to a boil and skim the froth. Add 1/2 cup cold water, bring the mixture to a simmer, and skim any froth. Simmer the mixture, adding boiling water to keep the ingredients barely covered, for 5 to 6 hours, or until the stock is reduced to about 8 cups. Strain the stock through a fine sieve into a bowl, pressing hard on the solids, and let it cool. Chill the stock and remove the fat. The stock may be frozen. Makes about 8 cups. DEMIGLACE 8 cups brown stock (recipe precedes), chilled and skimmed of fat In a large saucepan cook the stock over moderate heat until it is reduced to about 4 cups. Let the demiglace cool, transfer it to small freezer containers, and store it, covered, in the freezer. To use the demiglace, dip a spoon in hot water and spoon out the desired amount. keeps frozen indefinitely. Makes about 4 cups. GLACE DE VIANDE 8 cups brown stock (recipe precedes) , chilled and skimmed of fat In a large saucepan cook the stock over moderate heat until it is reduced to about 2 cups and is syrupy. Let the glace de viande cool, transfer it to small freezer containers, and store it, covered, in the freezer. To use the glace de viande , dip a spoon in hot water and spoon out the desired amount. The glace de viande keeps, frozen, indefinitely. Makes about 2 cups.