Simmer the giblets very gently in the water with the onion (if liked) for at least 2 hr.—much longer if possible. Drain the fat from the tin in which the bird has been roasted, carefully saving the sediment. Dredge into the thin film of dripping only sufficient flour to absorb it all. Brown this flour until a nut brown colour. Stir in the liquid from the giblets, boil up and season to taste.