In mixing bowl, combine turkey, sour cream, soup, milk, 1/2 cup cheese, hash browns, and onion. Spread in bottom of greased 2-quart dish. Bake, uncovered, at 350 degrees for 1 hour. Add additional 1/2 cup of cheese and corn flake cereal, and bake another 5 to 10 minutes until bubbly and slightly browned. Let cool for 10 minutes.