01 - Sprinkle beef short ribs evenly with salt and black pepper on all sides.
02 - Heat a large skillet over medium-high. Brown short ribs on all sides for 2 to 3 minutes per side; transfer ribs to the slow cooker.
03 - In the same skillet, sauté onion, carrots, celery, and garlic for 3 to 4 minutes until slightly softened. Add vegetables to the slow cooker.
04 - Pour beef broth and red wine into the slow cooker. Stir in tomato paste and Worcestershire sauce until well incorporated.
05 - Place thyme sprigs, rosemary sprigs, and bay leaves into the slow cooker.
06 - Cover and cook on LOW for 8 hours, or until beef is extremely tender and pulls away from the bone easily.
07 - Remove and discard herb sprigs and bay leaves. Skim any excess fat from the cooking liquid if necessary.
08 - If a thicker sauce is desired, stir cornstarch slurry into the cooker, increase to HIGH, and cook for 10 to 15 minutes until the sauce thickens.
09 - Serve short ribs hot, spooning sauce and vegetables over the top.