Start by trimming any excess fat off the beef chuck roast. Cut it into large chunks if desired, but you can also leave it whole for a more traditional presentation.
In a small bowl, mix together the garlic powder, black pepper, and salt. Rub this mixture all over the beef to ensure it’s well-seasoned.
Place the beef chunks in the slow cooker. Pour in the beef broth, and sprinkle the onion soup mix over the top. Add the Worcestershire sauce, making sure everything is well combined.
Cover the slow cooker and set it to low for 8 hours or high for 4 hours. The longer, slower cooking time is ideal for achieving that melt-in-your-mouth texture.
Once the cooking time is up, remove the beef from the slow cooker and set it aside. In a small mixing bowl, combine the cornstarch and cold water until smooth. Stir this mixture into the remaining juices in the slow cooker. Turn the slow cooker to high and let it cook for an additional 15-30 minutes, or until the gravy has thickened.
Slice or shred the beef as desired, then return it to the slow cooker to soak up more of that delicious gravy. Serve hot, garnished with fresh parsley.