1Break spaghetti into thirds and cook according to package directions. Drain.
While spaghetti is cooking, brown and drain ground beef and add spaghetti sauce. Add to drained spaghetti and layer half of spaghetti in a 9x13 baking dish. Set aside
2FOR CHEESE SAUCE
Put oil and flour in a 9-inch skillet. Stir over medium heat until it looks like thick glue not paste. You may need additional oil or flour to achieve the right consistency. This is your "gravy rue".
3Add evaporated milk and stir constantly with a fork remembering to scrape the bottom as gravy will build up. As it thickens add water and cook until it begins to thicken again.
4Quickly add parmesan and American cheese slices and stir until melted. Pour thickened cheese sauce gravy over spaghetti in pan and top with remaining spaghetti. Bake in 350 oven until hot throughout.