Dry the chuck roast and season with salt, pepper, and garlic powder.
Add onion to the bottom of the slow cooker. Place the beef on top.
Pour beef broth and Worcestershire sauce over the beef, then cover with the lid.
Cook on low for 6-8 hours or on high for 4-5 hours until beef is fork tender.
Remove beef from slow cooker and shred with two forks. Then return it to the slow cooker.
Add egg noodles to the slow cooker, cover, and cook on high for 20-30 minutes or until tender.
Whisk cornstarch and cold water together, add to the slow cooker, and continue cooking on high for 10 more minutes.
Add butter, season with additional salt and pepper, and serve.