Wipe and trim the meat and flatten it with a rolling-pin. Season the forcemeat well, spread it on the meat, and roll up tightly and tie securely. Heat the fat in a saucepan until very hot and fry meat quickly until the whole surface is browned. Add the hot stock or water, cover closely and cook very slowly for about 2 hr. When ready, place the meat on a hot dish. Thicken the gravy with the flour which has been blended to a smooth paste with a little cold stock or water and boil for 4 min. Season to taste, strain and pour some over the meat. Serve the remainder separately. If preferred, the roll may be baked in a moderate oven (350° F., Gas 4) in which case it must be well basted with stock or fat.