Place vegetable oil in a large skillet and place skillet over medium-high heat. Once hot, add chuck roast and sear for 3-4 minutes per side.
Using a large slow cooker, add minced garlic, diced onions, onion soup mix, beef stock, Worcestershire sauce, salt and pepper; stir until well combined.
Add chuck roast and cook on HIGH for 3-4 hours or LOW for 5-6 hours. Once the beef is fork tender - it should fall apart easily. Break roast into bite-sized pieces. Reserve 4 cups of cooking liquid from slow cooker to make gravy.
Meanwhile, cook egg noodles according to package instructions. Once cooked, drain noodles.
To serve, place egg noodles on a large plate and top with beef.
Pour several spoonsful of gravy on top of beef before serving.
Garnish with freshly chopped parsley before serving.
For the Gravy
Using a small bowl, add cornstarch and water; whisk together until well combined. Set bowl aside.
Using a large saucepan, add butter and place on stove top over medium-low heat. Once butter has melted, add flour; continue sautéing, stirring frequently, for 4-5 minutes or until mixture turns golden brown.
Add 4 cups of reserved liquid from the slow cooker along with the ketchup and apple cider vinegar; stir until well combined. Increase heat to medium-high and bring mixture to a boil.
Once boiling, add cornstarch slurry (from above). Using a whisk, stir until mixture is well combined.
Simmer over medium heat, stirring often, for 3-5 minutes, or until gravy thickens noticeably.