Roux is a mixture of fat and flour used as a thickening agent in cooking, particularly in sauces and soups. It is typically made by cooking equal parts of flour and fat, such as butter, over low heat until it reaches a desired color, which can range from pale blonde to dark brown. The color of the roux affects the flavor and thickness of the final dish. There are three main types of roux: white roux, blond roux, and brown roux. White roux is cooked for a short time and is used in creamy sauces like béchamel. Blond roux is cooked slightly longer and adds a nuttier flavor, while brown roux is cooked the longest, providing a rich, deep flavor suitable for dishes like gumbo.