01 - Place the sliced onions and minced garlic evenly across the bottom of the slow cooker.
02 - Set the beef chuck roast atop the onion and garlic layer.
03 - In a mixing bowl, whisk together beef broth, soy sauce, Worcestershire sauce, Dijon mustard, thyme, rosemary, and black pepper. Pour the mixture over the beef and add bay leaves.
04 - Cover and cook on low heat for 8 hours, or until the beef is very tender and shreds effortlessly.
05 - Transfer beef to a cutting board and shred using two forks. Discard any large pieces of fat.
06 - Strain the cooking liquid through a fine mesh sieve or fat separator into a bowl, discarding bay leaves and solids. Skim excess fat if desired. Reserve the strained liquid for dipping.
07 - Preheat broiler. Lightly spread butter on the cut sides of each roll and place them cut side up on a baking sheet. Broil for 1–2 minutes until golden and crisp.
08 - Layer shredded beef on the bottom halves of the toasted rolls. Top each with 2 slices of cheese. Broil for 1–2 minutes until the cheese is melted.
09 - Close with the top halves of the rolls. Serve immediately with individual bowls of warm au jus for dipping.