Day before: In large roasting pan, pour vinegar and the seasonings (season heavily) over beef. Brown, uncovered, for 1 hour at 350 degrees. Add 2 cups boiling water and beef broth to pan and place sliced onions on top. Cover and cook at 300 degrees for 4 to 5 hours. Cool. Refrigerate overnight. Slice into 1/4" slices, heat and serve in its own juices. Serves 20 and is great for buffets.