Sear the Beef: Heat the olive oil in a large skillet over medium-high heat. Season the beef with salt and pepper, then sear it on all sides until browned, about 3-4 minutes per side. Transfer the beef to the slow cooker.
Add Aromatics and Liquids: Add the sliced onion and minced garlic to the slow cooker. Pour the beef broth, Worcestershire sauce, and soy sauce over the beef. Sprinkle with dried thyme and rosemary for extra flavor.
Cook Low and Slow: Cover and cook on low for 6-8 hours, or until the beef is tender and easily shreds with a fork.
Shred the Beef: Once cooked, remove the beef from the slow cooker and shred it using two forks. Return the shredded beef to the slow cooker to soak in the flavorful au jus.
Toast the Rolls: Preheat the oven to 375°F (190°C). Slice the hoagie rolls or baguettes and place them on a baking sheet. Add a slice of provolone or Swiss cheese to each roll and toast in the oven for 3-5 minutes, until the cheese is melted and the bread is crispy.
Assemble the Sandwiches: Pile the shredded beef onto the toasted rolls and top with sautéed onions and mushrooms if desired.
Prepare the Au Jus: Strain the liquid from the slow cooker to remove any solids. Serve the au jus in small bowls for dipping.
Serve and Enjoy: Serve the sandwiches hot with a side of au jus for dipping.