01 - Evenly coat beef short ribs on all sides with salt and black pepper.
02 - Heat a large skillet over medium-high heat and sear the short ribs on each side for 2 to 3 minutes until well browned. Transfer ribs to the slow cooker.
03 - In the same skillet, sauté chopped onion, carrots, celery, and garlic for 3 to 4 minutes until vegetables are slightly softened. Transfer mixture to the slow cooker.
04 - Add beef broth and dry red wine to the slow cooker. Stir in tomato paste and Worcestershire sauce until fully combined.
05 - Nestle thyme, rosemary, and bay leaves into the slow cooker with the other ingredients.
06 - Cover the slow cooker and cook on LOW for 8 hours, or until the beef is extremely tender and detaches easily from the bone.
07 - Remove and discard herb sprigs and bay leaves. Skim off excess fat from the surface as needed.
08 - If a thicker sauce is desired, stir in a slurry of cornstarch and water. Set the slow cooker to HIGH and cook for an additional 10 to 15 minutes until the sauce thickens.
09 - Plate hot short ribs with the sauce and vegetables. Serve immediately.