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