In a large bowl, combine all the meatball ingredients (ground beef, eggs, breadcrumbs, Worcestershire sauce, garlic powder, onion powder, salt and pepper). Mix just until everything comes together uniformly - don't overmix it.
2 Lbs Ground Beef, 2 Large Eggs, 1 C Breadcrumbs, 2 Tbsp Worcestershire Sauce, 1 tsp Garlic Powder, 1 tsp Onion Powder, Salt and Pepper to Taste
Roll those mixture into meatballs of 1.25-1.5 inches in diameter (you should get between 30-40 meatballs). Alternatively, you could form the meat mixture into 8 even-sized oval patties - the traditional Salisbury steak shape. They will cook just like the meatballs in the following steps. Note: you can make these meatballs the night before and refrigerate them raw - so you can pop them in the slow cooker before going to work. Optional Step: right before adding everything to the slow cooker, you can sear the meatballs/patties to get a little more color and flavor. This step is great if you have a multicooker, because you can simply switch to slow cooking after searing the meat. If you are using a slow cooker, you can sear the meat in a separate pan and then deglaze the pan with the broth used in the following step. For the gravy, mix together the beef broth, Worcestershire sauce, onion soup mix, ketchup and mustard.
2 C Beef Broth, 1 Tbsp Worcestershire Sauce, 2 Tbsp Ketchup, 1 tsp Mustard, 1 1 Oz. Packet Onion Soup Mix
In your slow cooker/multicooker, layer the (optional) onions and mushrooms in the bottom. Then add the meatballs/patties, doing your best to keep them in a single layer. Pour the gravy mixture evenly over the top.
1 C Mushrooms, Sliced, 1 Small Onion, Thinly Sliced
Slow cook on high for 4-5 hours, or low for 8-10 hours.
To finish the gravy, make a slurry by mixing the corn starch and water in a small bowl. Pull the meat out of the slow cooker and add the corn starch slurry to the gravy (and optional onions and mushrooms).
2 Tbsp Corn Starch, 2 Tbsp Water
Let the gravy cook uncovered for another 10-15 minutes, stirring occasionally, until it thickens from the corn starch. If using a slow cooker, turn it to high for this. In a multicooker, set it to sauté or something similar. Taste the gravy for salt and pepper.
Mix the meat back in the with gravy and serve! The meatballs are great appetizers. You can also serve them (or the patties) over mashed potatoes, egg noodles or rice for a full main course.