2 1/2 lb. boneless beef brisket
1/2 c. water
1 tbsp. cider vinegar
1 1/2 tsp. white horseradish
1 1/2 tsp. prepared mustard
1/2 c. ketchup
1 1/2 tsp. instant minced onions
1/2 tsp. salt
1/8 tsp. pepper

Place beef in casserole, fat side up. Mix all other ingredients together and pour over beef. Cover tightly and bake in a 300 degree oven until tender, about 3 1/2 hours. Refrigerate beef and gravy separately overnight. Slice beef very thin and arrange in glass baking dish. Remove hardened fat from gravy and pour gravy over sliced beef. Cover tightly with foil and reheat in preheated 350 degree oven until bubbling hot, about 30 minutes. Serves 4.