This recipe for homemade beef stock, courtesy of Martha's personal chef Pierre Schaedelin, is an excellent marinade for braised short ribs.
Heat oil in a large Dutch oven over medium-high heat. Add bones and brown on all sides, about 5 minutes. Add onion, carrot, celery, and garlic; cook until lightly browned, about 5 minutes more.
Add 10 cups of water and bring to a boil. Immediately reduce to a simmer, cover, and cook 1 1/2 hours. Skim surface and strain stock before using.