In a large bowl, mix together the beef, Worcestershire sauce, breadcrumbs, milk, and season with salt and pepper.
Form the meat mixture into equal-sized oval-shaped patties.
In a large nonstick pan over medium heat, sear both sides of the patties until they are browned and set them aside on a plate.
Melt the butter in the pan. Add the onion and mushrooms and season with salt and pepper.
Cook for 3 to 5 minutes or until vegetables have softened. Add in the flour and cook while stirring for 1 minute. Add the beef broth and bring to a simmer. Add Salisbury steaks back into the pan and simmer for 15 minutes.
The sauce should be a thickened smooth consistency. Remove from the heat when the gravy has reached the desired thickness. Season the gravy with salt and pepper to taste and sprinkle with parsley to garnish. Serve with crusty bread.