Step 1: Prepare the Ingredients

1. Chop the Onion: Finely chop 1 medium onion. This will add a slight sweetness and extra flavor to the gravy. If you prefer a milder onion flavor, you can substitute with shallots.
2. Slice the Mushrooms: If using fresh mushrooms, slice them thinly. You can also use canned mushrooms—just make sure to drain them well.
3. Make the Gravy Base: In a mixing bowl, whisk together the beef broth, cream of mushroom soup, Worcestershire sauce, soy sauce, ketchup, garlic powder, onion powder, salt, and black pepper. This mixture will create the rich, savory base that turns into gravy as it cooks with the meatballs.

Step 2: Add Ingredients to the Slow Cooker

1. Layer the Onion and Mushrooms: Place the chopped onions and sliced mushrooms in the bottom of your slow cooker. These will release moisture and flavor as they cook, adding depth to the gravy.
2. Add the Frozen Meatballs: Place the frozen meatballs on top of the onion and mushroom layer. No need to thaw them; just add them straight from the freezer.
3. Pour the Gravy Mixture: Pour the prepared gravy mixture over the meatballs, making sure they’re evenly coated.
4. Gently Stir: Use a spoon to gently mix the meatballs and gravy, ensuring all the meatballs are coated but trying not to break them up.

Step 3: Cook the Meatballs

1. Set the Slow Cooker: Cover the slow cooker with the lid and set it to low for 4-5 hours or high for 2-3 hours. Cooking on low allows the flavors to meld together more slowly, but either option works well depending on your schedule.
2. Check for Doneness: After the cooking time is up, check to see if the meatballs are heated through and tender, and the gravy has thickened slightly. The meatballs should be warm all the way through and nicely coated in gravy.

Step 4: Thicken the Gravy (Optional)

1. Combine Cornstarch and Water: If you’d like a thicker gravy, whisk together 2 tablespoons of cornstarch with 2 tablespoons of water in a small bowl until smooth.
2. Add to Slow Cooker: Pour the cornstarch mixture into the slow cooker and stir well to combine with the gravy.
3. Cook for 15-20 More Minutes: Cover and cook on high for an additional 15-20 minutes until the gravy reaches your desired thickness.

Step 5: Serve and Garnish

1. Serve the Meatballs: Spoon the Salisbury steak meatballs onto a plate or into a bowl along with a generous helping of gravy.
2. Garnish: For an extra touch of freshness, sprinkle chopped fresh parsley or thyme leaves on top.