Beef Osso Bucco

In a large resealable container, combine the flour, 1/2 teaspoon salt and pepper. Add beef, a few pieces at a time, and shake to coat., In a large skillet, brown beef in butter and oil. Transfer meat and drippings to a 6-qt. slow cooker. Add wine to skillet, stirring to loosen browned bits from pan; pour over meat. Add the tomatoes, broth, carrots, onion, celery, thyme, oregano, bay leaves and remaining salt., Cover and cook on low for 7-9 hours or until meat is tender. Discard bay leaves., Skim fat from cooking juices; transfer juices to a large saucepan. Bring to a boil. Combine cornstarch and water until smooth; gradually stir into the pan. Bring to a boil; cook and stir for 2 minutes or until thickened., In a small bowl, combine the gremolata ingredients. Serve beef with gremolata and sauce. If desired, serve over polenta.