01 - Arrange the thinly sliced onion and minced garlic evenly across the bottom of a 6 to 8 quart slow cooker.
02 - Season the beef chuck roast on all sides with black pepper, then place it on top of the onion and garlic bed.
03 - In a mixing bowl, whisk together the beef broth, soy sauce, Worcestershire sauce, dried thyme, dried rosemary, and bay leaf until well combined. Pour the mixture over the beef.
04 - Cover the slow cooker and cook on the low setting for 8 hours, or until the beef is fork-tender and pulls apart easily.
05 - Carefully remove the beef from the slow cooker and transfer to a cutting board. Shred using two forks, discarding any excess fat or connective tissue. Remove and discard the bay leaf from the cooking liquid.
06 - Set the oven to broil. Arrange the French rolls open-faced on a baking sheet.
07 - Divide the shredded beef evenly among the rolls. Top each sandwich with a slice of provolone or Swiss cheese, if desired.
08 - Place the baking sheet under the broiler for 1 to 2 minutes, until the cheese is fully melted and the rolls are lightly toasted. Watch closely to prevent burning.
09 - Pour the remaining cooking liquid through a strainer into individual serving bowls, creating the au jus for dipping.
10 - Serve the hot sandwiches immediately, each accompanied by a bowl of warm au jus for dipping.