In a medium-size bowl, combine together ground beef, breadcrumbs, ketchup, Worcestershire sauce, mustard powder, egg, and salt & pepper. Combine together with your hands and shape into 4 oval Salisbury Steak patties about 1 inch thick.
Heat saute skillet up a little and add butter over medium heat. Add the Salisbury Steak patties and cook until sides are seared on both sides. Remove from heat and set aside on a plate.
Add olive oil to heated saute skillet, then add in mushrooms and onions, cook until almost tender.
Add in the beef broth, minced garlic, ketchup, and Worchestershire sauce, Heat to a slow boil, sift in the flour, and whisk to a boil. Reduce heat to low and add the Salisbury Steak Patties back into the skillet.
Place a lid on the skillet and simmer until the brown gravy is as thickness you want it.
Serve with Noodles, Potatoes, Pasta, Vegetable. Enjoy!