Midwest Salisbury Steak

Midwest Salisbury Steak Patties1 pound ground sirloin1/2 cup panko bread crumbs1 egg (beaten)2 tablespoons milk1/2 package DRY ONION SOUP MIX1 teaspoon Worcestershire sauce1/4 teaspoon black pepperGravy3 tablespoons butter2 cups fresh mushrooms (sliced)1 sweet onion...