01 - Coat beef cubes evenly with salt and pepper on all sides.
02 - Heat a large skillet over medium-high heat. Working in batches to avoid crowding, brown the beef on all sides until deeply caramelized, approximately 5-7 minutes per batch. Transfer browned beef to the slow cooker.
03 - Place carrots, potatoes, onion, garlic, and celery into the slow cooker with the browned beef.
04 - In a mixing bowl, whisk together beef broth, tomato paste, Worcestershire sauce, and red wine if using until well combined. Pour the liquid over the beef and vegetables in the slow cooker.
05 - Sprinkle thyme, rosemary, and bay leaves over the mixture. Stir thoroughly to distribute seasonings evenly.
06 - Cover the slow cooker and cook on LOW setting for 7 to 8 hours, or on HIGH setting for 4 to 5 hours, until beef is fork-tender and vegetables are completely cooked through.
07 - During the final 30 minutes of cooking, combine cornstarch and cold water in a small bowl, stirring until smooth and lump-free. Pour the slurry into the stew and stir well to thicken the broth.
08 - Remove and discard bay leaves. Taste the stew and adjust salt, pepper, or seasonings as needed.
09 - Ladle the stew into bowls and garnish with fresh parsley. Serve hot.