01 - Pat beef cubes dry with paper towels and season evenly with salt and black pepper.
02 - Heat a large skillet over medium-high heat and sear beef in batches until browned on all sides, then transfer to slow cooker.
03 - Place carrots, potatoes, celery, onion, and garlic into the slow cooker with the beef.
04 - In a bowl, whisk together beef broth, tomato paste, Worcestershire sauce, red wine if using, dried thyme, and dried rosemary.
05 - Pour broth mixture over beef and vegetables in slow cooker; add bay leaves. Cover and cook on LOW for 8 hours or HIGH for 4 to 5 hours until beef and vegetables are tender.
06 - Mix cornstarch and cold water until smooth and stir into stew. Cover and cook on HIGH for 15 to 20 minutes until thickened.
07 - Remove bay leaves, taste, and adjust seasoning as needed.
08 - Sprinkle with chopped fresh parsley before serving.