To make Turkey gravy first make a raw roux. Unbleached flour is normally used, but rice flour can be substituted to make this gluten free. Allow it to cook for a moment and then slowly add the cold water. Whisk consistently until there are no lumps and you have a fine slurry. Add the turkey stock and stir. Turn down the heat. Add chicken stock if desired or necessary until the gravy has a rich, full mouth feel. Add the corn starch to cold water and mix well. Slowly add the corn starch slurry to the gravy. Allow to gently simmer for ten minutes, occasionally stirring.