Creating your Slow Cooker Beef Manhattan is straightforward if you follow these simple steps:

1. Sear the Beef: Heat olive oil in a skillet over medium-high heat. Season the beef chuck roast with salt and pepper, then sear it on all sides until browned (about 3-4 minutes per side).
2. Chop the Vegetables: While the beef is searing, chop the onion and garlic. Slice the mushrooms if using.
3. Prepare the Slow Cooker: In your slow cooker, place the chopped onion, minced garlic, and sliced mushrooms.
4. Add the Beef: Once the beef is seared, place it on top of the vegetables in the slow cooker.
5. Add the Broth and Sauces: Pour in the beef broth, Worcestershire sauce, soy sauce, dried thyme, salt, and pepper.
6. Set It & Forget It: Cover and cook on low for 8-10 hours or high for 4-6 hours until the beef is tender.
7. Thicken the Gravy (Optional): If you desire a thicker gravy, remove 1 cup of liquid from the slow cooker and mix it with cornstarch in a small bowl. Return to the slow cooker and stir until well combined. Let it cook for an additional 30 minutes.
8. Toast the Bread: While the beef is finishing, toast the slices of bread until golden brown.
9. Serve the Dish: Cut the beef into slices or shred it with two forks. Pile the beef and gravy over the toasted bread.
10. Garnish: If desired, sprinkle with chopped fresh parsley before serving.

Following these steps will guide you toward creating this deliciously comforting meal effortlessly.