Pat the chuck roast dry and season it with salt, black pepper, and garlic powder.
Place the diced onion in the bottom of the slow cooker, then set the seasoned beef chuck roast on top.
Pour the beef broth and Worcestershire sauce over the beef. Cover the slow cooker with the lid.
Cook on low for 6–8 hours or on high for 4–5 hours, until the beef is fork-tender.
Remove the beef from the slow cooker and shred it thoroughly using two forks. Return the shredded beef to the slow cooker.
Add the frozen egg noodles, cover, and cook on high for 20–30 minutes, or until the noodles are tender.
If using the optional thickener, whisk the cornstarch and cold water together. .
Add the mixture to the slow cooker and continue cooking on high for 10 more minutes.
Stir in the optional butter, season with additional salt and pepper to taste, and SERVE
