Spread flour about I inch thick across the bottom of an iron pot, baking pan or cookie sheet. Bake at 400 degrees for I to 1 1/2 hours. Stir occasionally, being sure to stir in the flour from along the edges and corners. Cook until light brown or darker. When water is added, it will darken even more. Remove the amount of flour your recipe calls for to make a roux. Store the rest in zippered plastic bags for future recipes. To the portion using, slowly stir in an equal amount of cold water and form a smooth paste. Stir this paste gradually into the simmering stock, soup, gumbo, etc. Cook for at least 20 minutes, stirring occasionally.