1In a large bowl, combine the ground beef, breadcrumbs, milk, finely chopped small onion, egg, Worcestershire sauce, salt, and black pepper. Mix until well combined.
Shape the mixture into 4-6 oval patties.
In a large skillet over medium-high heat, cook the patties until browned on both sides, about 4-5 minutes per side. Remove the patties from the skillet and set aside.
In the same skillet, add the sliced large onion and cook until softened and lightly browned, about 5-7 minutes.
In a small bowl, mix the cornstarch and water to create a slurry.
Add the beef broth to the skillet with the onions and bring to a simmer. Stir in the cornstarch slurry and cook until the gravy thickens, about 2-3 minutes.
Return the patties to the skillet and spoon the onion gravy over them. Simmer for an additional 5-7 minutes, or until the patties are cooked through.
Serve the Salisbury steak with onion gravy hot, garnished with additional black pepper if desired.