In a large mixing bowl, add ground beef, Panko bread crumb, egg, ketchup, mustard powder, Worcestershire sauce, steak seasoning, black pepper, onion powder and salt.
Knead until completely combined and form into medium sized meatballs. For this recipe, I just use ½ cup spoon and mold the meat into meatballs.
Heat a large skillet or dutch over medium heat. Add the meatballs and gently move around the pan to brown. Transfer the meatballs to the slow cooker.
Using the same skillet, add butter and cook onions for about 3-4 minutes until softened. Transfer them to the slow cooker.
Add mushrooms, ketchup, broth and Worcestershire sauce into the slow cooker and cook for about 2-3 hours on high or 4-5 hours on low.
In a small bowl, beat cornstarch and cold water. Quickly stir and pour the mixture into slow cooker and increase the heat to high until the sauce is thicken. Cook for about 5-10 minutes. Serve with Idaho Spuds VeggieMash and chopped parsley.
