Place the diced potatoes, carrots, celery, onion, and minced garlic into the bottom of the slow cooker.
Add the beef chuck roast cubes directly on top of the vegetables.
In a medium bowl, whisk together the beef broth, tomato paste, Worcestershire sauce, salt, and black pepper. Pour this mixture evenly over the beef and vegetables.
Cover and cook on LOW for 7 to 8 hours, or on HIGH for 4 to 5 hours, until the beef is remarkably tender.
Thirty minutes before the stew is done cooking, whisk the cornstarch and water together in a small bowl to create a slurry. Stir the slurry into the slow cooker to thicken the broth.
Cover and cook for the remaining 30 minutes. Garnish with freshly chopped parsley and serve warm.