In a mixing bowl, combine ground beef, breadcrumbs, chopped onion, milk, egg, Worcestershire sauce, salt, and pepper. Mix until well combined.

Divide the mixture into 4-6 portions and shape them into oval patties.

Heat a skillet or frying pan over medium-high heat. Cook the patties for about 4-5 minutes per side or until browned and cooked through. Once done, remove them from the pan and set aside.

In the same pan, add 2 tablespoons of butter and sauté the sliced onions until they are soft and golden brown.

Sprinkle flour over the onions and stir to combine. Cook for 1-2 minutes to remove the raw taste of the flour.

Gradually whisk in beef broth, Worcestershire sauce, salt, and pepper. Allow the mixture to simmer and thicken, stirring frequently.

Once the gravy has thickened, return the cooked patties to the pan. Spoon some of the gravy over the patties and let them simmer in the sauce for an additional 5-7 minutes.

Serve the Salisbury Steak patties with the onion gravy over mashed potatoes, rice, or noodles.