In a medium-sized bowl, mix ground beef, egg, panko breadcrumbs, A1 steak sauce, Worcestershire sauce, ketchup, steak seasoning, garlic powder, and onion powder. Use your hands to blend everything well. Shape into 4 round patties, about ¾ to 1 inch thick.

Heat 1 tablespoon of butter in a medium skillet over medium heat. Cook the patties for 5 minutes on each side until thoroughly cooked. Remove from skillet and keep warm.

If necessary, discard excess grease from the skillet, leaving about 1 tablespoon. Add 3 tablespoons of butter and scrape up bits from the bottom.

Add sliced onions and cook for 5 minutes until translucent.

Stir in the flour and cook for about 2 minutes until slightly browned.

Slowly add the beef broth while stirring until smooth. Cook for 3 to 4 minutes until gravy thickens. Season with salt and pepper.

Add sliced mushrooms and cooked patties back into the skillet. Reduce heat and simmer for 7 to 10 minutes until mushrooms are tender.

Serve Salisbury Steak hot with sides like mashed potatoes, rice, or vegetables.