Place ground beef, breadcrumbs, egg, Worcestershire sauce and seasonings inside a large bowl. Mix gently until combined evenly.

Form the beef mixture into oval patties. Make each patty similar in size for even cooking results.

Place a large skillet over medium heat. Add olive oil and allow it to heat completely before cooking.

Add beef patties into the skillet carefully. Cook both sides until nicely browned but not fully cooked inside.

Transfer browned patties onto a plate. Keep the flavorful juices inside the skillet for making rich gravy later.

Add butter and sliced onions into the skillet. Cook slowly until onions become soft, golden, and slightly caramelized.

Sprinkle flour over the onions evenly. Stir continuously for one minute to remove the raw flour taste completely.

Slowly add beef broth while stirring constantly. This keeps the gravy smooth without lumps forming inside the skillet.

Mix ketchup and Dijon mustard into the gravy. Stir well until the sauce becomes rich and fully combined.

Place beef patties back into the skillet carefully. Spoon some gravy over each patty to keep them moist.

Cover the skillet and simmer for fifteen minutes. The patties will finish cooking while absorbing delicious gravy flavor.

Sprinkle fresh parsley over the Salisbury steak. Serve hot with mashed potatoes, rice, or buttered noodles.