Season the chuck roast on all sides with salt and pepper. Place the sliced onion in the bottom of the slow cooker, then set the roast on top.

Pour in the beef broth and Worcestershire sauce. Add the bay leaf. Cover and cook on low for 8 hours until the beef shreds easily with a fork.

While the beef cooks, roast the garlic. Preheat the oven to 400°F. Wrap the whole garlic cloves in foil and roast for 30 minutes until soft. Let them cool, then squeeze out the cloves and mash with a fork.

When the beef is done, remove it from the slow cooker and shred or slice it. Strain the cooking liquid into a saucepan, discarding the solids. Stir the mashed roasted garlic into the liquid and simmer for 5 minutes to make the au jus.

Split the French rolls and divide the beef among them. Top each with two slices of provolone. Place under the broiler for 1 to 2 minutes until the cheese melts.

Serve the sandwiches with small bowls of the roasted garlic au jus for dipping.