Brown and drain ground beef. Saute onion till lightly brown. Fry potatoes and drain on paper towel.
Mix ground beef, 1 cup cheese and ketchup together in bowl. Lay pie shell out flat and spoon some of the beef mixture onto crust. Add potatoes and a little more cheese on top. Then fold pie crust over filling.
Bake at 400 degrees F until crust is golden brown, around 15 minutes.