Preheat the oven to 400°F (200°C).

In a large bowl, mix the ground beef, bread crumbs, chopped onion, egg, Worcestershire sauce, garlic powder, and season with salt and pepper. Use your hands to combine everything.

Shape the mixture into generous meatballs, about 1.5 inches in diameter.

Place the meatballs on a baking sheet and pop them in the oven. Bake for about 20 minutes until they are beautifully browned and cooked through.

While the meatballs bake, prepare the mushroom gravy. In a skillet over medium heat, melt the butter and sauté the finely chopped onion until they turn translucent.

Add the sliced mushrooms to the skillet and cook until they are soft.

Sprinkle the flour over the mushrooms, stirring well to combine. Gradually pour in the beef broth while stirring constantly.

Season the gravy with salt and pepper to taste. Allow it to simmer until thickened, about 5-7 minutes.

Once the meatballs are done, gently place them into the skillet with the gravy, allowing them to soak up that rich flavor for a minute or two.

Serve these delightful Salisbury steak meatballs over mashed potatoes or rice.