Pat the chuck roast dry with paper towels. In a small bowl, mix together the salt, pepper, garlic powder, and onion powder, then rub the mixture all over the surface of the roast on all sides.

Place the sliced onions and minced garlic in the bottom of the slow cooker insert. Lay the seasoned chuck roast on top of the onions.

Pour the beef broth, Worcestershire sauce, and soy sauce over and around the roast. Sprinkle the onion soup mix (if using), dried thyme, and dried rosemary evenly over the top.

Place the lid on the slow cooker. Cook on LOW for 8 to 9 hours, or on HIGH for 4 to 5 hours, until the beef is completely fork-tender and easily falls apart when pulled with two forks. Do not lift the lid during cooking.

Once cooked, transfer the beef to a cutting board or large bowl. Use two forks to shred the meat, discarding any large pieces of fat. Return the shredded beef to the slow cooker and stir to combine with the cooking liquid.

In a small bowl, whisk together the cornstarch and cold water until completely smooth to form a slurry.

Stir the cornstarch slurry into the slow cooker with the shredded beef and braising liquid. Switch the slow cooker to HIGH, replace the lid, and cook for an additional 20 to 30 minutes, stirring once or twice, until the gravy has thickened to your desired consistency. Stir in the butter if using.

Taste the gravy and adjust seasoning with additional salt and pepper as needed.

While the gravy thickens, bring a large pot of salted water to a boil and cook the wide egg noodles according to package directions until just al dente. Drain well.

Divide the cooked egg noodles among bowls or plates. Spoon a generous portion of the shredded beef and gravy over the noodles. Garnish with fresh chopped parsley and serve immediately.