Salisbury Steak with Onion Gravy

I make this dish from time to time and it always turns out wonderful. It is great served with mashed potatoes and a vegetable.

1 can condensed french onion soup
1-1/2 lbs ground beef
1/2 cup seasoned bread crumbs
1 egg
1/4 teaspoon salt, a dash of pepper
3 Tablespoons flour
1/4 cup ketchup
3 cups water
1 teaspoon Worcestershire sauce
1/2 teaspoon yellow mustard

In a large bowl, combine 1/3 cup of the soup with beef, crumbs, egg, and seasoning. Shape into 6 oval patties. Brown in a skillet, drain off fat. In a small bowl, gradually blend the remaining soup into the flour until smooth. Add to the skillet with the remaining ingredients. Stir to loosen brown bits in the pan. Cover and cook on low heat for 20 minutes, stirring occasionally. You may need to adjust liquid to obtain a nice gravy consistency. Serves 6