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

1. Season the Beef: Start by seasoning the beef chuck roast with salt, pepper, garlic powder, and onion powder on all sides.
2. Sear the Meat: In a skillet over medium-high heat, sear the seasoned beef for 3 to 4 minutes on each side until browned. This step enhances the flavor but can be skipped if you’re in a hurry.
3. Place Ingredients in the Slow Cooker: Transfer the seared beef to the slow cooker. Add the sliced onion, mushrooms (if using), Worcestershire sauce, and beef broth.
4. Cook the Beef: Cover the slow cooker and cook on low for 6 to 8 hours or high for 4 to 5 hours until the beef is tender and easily shredded with a fork.
5. Thicken the Gravy: About 30 minutes before serving, mix the cornstarch with water in a small bowl until smooth. Stir this mixture into the pot, cover again, and allow the gravy to thicken.
6. Prepare the Bread: Toast the slices of bread while the gravy thickens, making sure they are warm and crispy.
7. Shred the Beef: Once the cooking time is complete, remove the beef and shred it using two forks. Return the shredded beef to the slow cooker, mixing it with the gravy.
8. Assemble the Dish: For serving, spoon the beef and gravy mixture onto the toasted bread. Top with your favorite toppings, such as sautéed onions, cheese, or fresh herbs.

These simple steps will provide a delightful dinner that your family will love!