01 - Generously season beef short ribs with salt and black pepper on all sides.
02 - Heat a large skillet over medium-high heat and sear the short ribs on every side for 2–3 minutes per side until deeply browned. Transfer ribs to slow cooker.
03 - In the same skillet, add chopped onion, carrots, celery, and minced garlic. Sauté for 3–4 minutes until slightly softened, then transfer vegetables to the slow cooker.
04 - Pour beef broth and red wine into the slow cooker. Stir in tomato paste and Worcestershire sauce until combined.
05 - Place thyme, rosemary sprigs, and bay leaves in the slow cooker.
06 - Cover and cook on low heat for 8 hours until the short ribs are exceptionally tender and meat easily falls off the bone.
07 - Discard thyme, rosemary sprigs, and bay leaves. Skim excess fat from the sauce, as needed.
08 - For a thicker sauce, whisk together cornstarch and water. Stir slurry into the slow cooker, switch to high heat, and cook for an additional 10–15 minutes until the sauce thickens.
09 - Plate short ribs with vegetables and spoon sauce over the top. Serve hot.