01 - Sprinkle beef short ribs with salt and black pepper on all sides.
02 - In a large skillet over medium-high heat, sear the short ribs on all sides for 2 to 3 minutes per side. Transfer browned ribs to the slow cooker.
03 - Add chopped onion, carrots, celery, and minced garlic to the skillet. Cook for about 3 to 4 minutes, stirring frequently, until the vegetables begin to soften. Transfer to the slow cooker.
04 - Pour beef broth and dry red wine into the slow cooker. Stir in tomato paste and Worcestershire sauce. Add thyme sprigs, rosemary sprigs, and bay leaves.
05 - Cover and cook on LOW for 8 hours, or until beef short ribs are extremely tender and meat pulls away from the bone.
06 - Remove thyme and rosemary sprigs and bay leaves. Skim excess fat from the surface, if necessary. For a thicker sauce, combine cornstarch with water and stir the mixture into the slow cooker. Cook on HIGH for another 10 to 15 minutes, until sauce has thickened.
07 - Serve hot short ribs with their sauce and vegetables ladled over each portion.