01 - In a large skillet over medium-high heat, brown beef cubes in batches for 2-3 minutes per side to develop flavor. Transfer browned beef to the slow cooker.
02 - Place potatoes, carrots, onion, garlic, and celery into the slow cooker with the beef.
03 - Whisk together beef broth, red wine if using, tomato paste, thyme, rosemary, bay leaves, salt, pepper, and Worcestershire sauce. Pour mixture over beef and vegetables.
04 - Stir gently to combine. Cover and cook on LOW for 8 hours or on HIGH for 4-5 hours, until beef and vegetables are tender.
05 - About 30 minutes before serving, mix cornstarch with cold water to form a slurry. Stir into stew to thicken. Remove and discard bay leaves.
06 - Taste and adjust seasoning if needed. Garnish with chopped fresh parsley prior to serving, if desired.