1Season the roast — Evenly season the chuck roast on all sides with garlic powder, onion powder, black pepper, and buttery garlic & herb seasoning.
2Sear the roast — Melt 4 tbsp of butter in a large skillet over medium-high heat. Add the chuck roast and sear for 2-3 minutes per side, or until nicely browned. Transfer the roast to your slow cooker.
3Add the liquids — Sprinkle the au jus gravy mix and beefy onion soup mix over the roast. Add the Worcestershire sauce and chicken broth.
4Caramelize the onions — In the same skillet, melt 2 tbsp of butter. Add the sliced onion and cook over medium heat for about 15 minutes, stirring occasionally, until softened and lightly caramelized.
5Top with onions — Spoon the onions directly over the roast. Cover and cook on LOW for 7-8 hours, or until the beef is fall-apart tender.
6Shred the beef — Remove the roast from the slow cooker and shred it with two forks. Return the beef to the slow cooker and toss it with some of the onions and juices.
7Assemble sandwiches — Pile the shredded beef and onions onto your buns and top with provolone cheese. For extra melty cheese, pop the assembled sandwiches under the broiler for a minute or two.
8Serve with au jus — Ladle some of the cooking liquid from the slow cooker into small bowls and serve alongside the sandwiches for dipping.