Heat the oven to 325°F.  Grate 1 teaspoon zest from the lemon.Heat the olive oil in a roasting pan over medium-high heat. Add the beef and cook until well browned on both sides. Remove the beef from the pan.  Pour off all but 1 tablespoon pan drippings.Reduce the heat to medium.  Add the garlic to the pan and cook until golden, stirring occasionally.  Add the vinegar to the pan and cook and stir for 1 minute, scraping up the browned bits from the bottom of the pan.  Stir in the stock, thyme and rosemary sprigs.  Reduce the heat to low.  Cook for 5 minutes.  Season with black pepper.Return the beef to the pan.  Spoon the stock mixture over the beef.  Cover the pan.Bake for 2 1/2 hours or until the beef is fork-tender. Baste the beef with the pan juices every 30 minutes.  Remove the beef from the pan, cover and keep warm.Strain the pan drippings through a sieve into a medium bowl, reserving the garlic and discarding the thyme and rosemary sprigs. Spoon off any fat.Place about half the garlic cloves and about 1 cup pan drippings into a food processor or blender.  Cover and process until the mixture is smooth.Heat the garlic mixture, remaining garlic cloves, remaining pan drippings, chopped rosemary, minced garlic and lemon zest in a 10-inch skillet over medium-high heat to a boil.  Cook and stir until the gravy is thickened.  Serve the gravy with the beef.