1. 1. Prepare the Beef: Trim any large excess fat from the beef chuck roast. If your roast is very large, you can cut it into 2-3 smaller pieces to help it fit better in the slow cooker and cook more evenly. Place the beef pieces directly into the bottom of your slow cooker insert.

2. 2. Add the Aromatics: Sprinkle the chopped onion over and around the beef in the slow cooker. The onion will soften and meld into the sauce, adding a foundational layer of flavor.

3. 3. Whisk the Sauce Ingredients: In a medium bowl, combine the beef broth, BBQ sauce, apple cider vinegar, Worcestershire sauce, brown sugar, garlic powder, smoked paprika, and black pepper. Whisk everything together until the brown sugar is dissolved and the sauce is well combined.

4. 4. Pour Over Beef: Carefully pour the prepared BBQ sauce mixture evenly over the beef and onions in the slow cooker. Ensure the beef is mostly submerged in the liquid.

5. 5. Cook Until Tender: Cover the slow cooker with its lid. Cook on the LOW setting for 6-8 hours, or on the HIGH setting for 3-4 hours. The beef is ready when it is fork-tender and easily shreds apart. You should be able to pull it apart with two forks with very little resistance.

6. 6. Shred the Beef: Once cooked, carefully remove the beef from the slow cooker and place it on a large cutting board or in a shallow dish. Using two forks, shred the beef into bite-sized pieces. Discard any remaining large pieces of fat or gristle.

7. 7. Return to Sauce: Place the shredded beef back into the slow cooker with the cooking liquid. Stir well to coat all the shredded beef thoroughly with the delicious BBQ sauce. Let it simmer on the WARM setting for another 15-30 minutes to allow the flavors to meld even further and the beef to absorb more sauce.

8. 8. Assemble Sandwiches: Toast your hamburger buns if desired. Spoon a generous amount of the BBQ pulled beef onto each bun. Serve immediately and enjoy!