Rub the meat thoroughly with the salt and pepper and put in an earthen dish. Add the onion, bay leaves and peppercorns. Take equal parts of vinegar and water and pour over the meat. Let stand in this liquid for 24 hours. Put meat in a roasting pan and sear well in oven at 400-F. When well browned, add a little of the spiced vinegar. Cover pan tightly and cook slowly for 3-1/2 hours or until meat is tender. Add more of the vinegar if necessary. When cooked, remove meat to a platter and thicken liquid with 1 Tbsp flour.