1Remove marrow from centers of bones. In 4-quart Dutch oven or stockpot, melt marrow over low heat until hot, or heat 2 tablespoons oil. Cook beef shanks in marrow or oil over medium heat until brown on both sides.
2Add water; heat to boiling. Skim foam from broth. Stir in remaining ingredients; heat to boiling. Skim foam from broth; reduce heat. Cover; simmer 3 hours.
3Remove beef from broth. Cool beef about 10 minutes or just until cool enough to handle. Strain broth through fine strainer; discard vegetables and seasonings.
4Remove beef from bones. Cut beef into 1/2-inch pieces. Skim fat from broth. Use broth and beef immediately, or cover and refrigerate broth and beef in separate containers up to 24 hours or freeze up to 6 months.