Begin by cutting your beef chuck roast into larger chunks, about 2-3 inches in size. If desired, heat a skillet over medium-high heat and brown the beef on all sides for 3-4 minutes.

In your slow cooker, add the beef chunks along with the onion soup mix, brown gravy, and apple cider vinegar. Stir well to ensure the beef is evenly coated with the mixture.

Cover the slow cooker and set it to LOW for 6-8 hours or HIGH for 3-4 hours until the beef is fork-tender.

If you prefer a thicker gravy, mix 2 tablespoons of cornstarch with 2 tablespoons of cold water and stir it into the slow cooker during the last 30 minutes of cooking.

Once your beef is tender, shred the beef directly in the slow cooker and serve over a bed of creamy mashed potatoes with gravy.