Creating the tender, flavorful Slow Cooker Beef Manhattan is simple. Just follow these steps:

1. Prepare the Beef: Trim excess fat from the beef chuck roast and season generously with salt and black pepper.
2. Place Ingredients in Slow Cooker: Add the beef roast to the slow cooker. Sprinkle onion soup mix over the top.
3. Add Broth: Pour the beef broth over the roast. Add Worcestershire sauce and garlic powder to enhance the flavor.
4. Add Vegetables: If using, layer sliced mushrooms and chopped onions around the beef for extra taste.
5. Add Potatoes: Place quartered potatoes on top of the other ingredients. They will tenderize beautifully while absorbing flavor.
6. Cover and Cook: Secure the lid on the slow cooker. Set to low and cook for 6-8 hours or high for 4-6 hours.
7. Check for Doneness: After cooking, check that the beef is tender and easily pulls apart with a fork.
8. Thicken the Gravy (Optional): If you prefer a thicker gravy, remove the beef and potatoes, then stir in a mixture of cornstarch and water to the liquid and heat until thickened.
9. Serve: Shred the beef if desired, then serve over mashed potatoes with gravy spooned on top.

These clear instructions will ensure you create a delicious Slow Cooker Beef Manhattan that will have everyone asking for seconds!