A roux is a cooked mixture of equal parts fat and flour used to thicken sauces, soups, and stews. It is one of the five mother sauces of French cuisine and is used as a base for many other sauces. Roux can be made with any type of fat, but butter and oil are the most common.
There are three main types of roux: white, blond, and brown. A white roux is cooked for a short period of time and has a light color. A blond roux is cooked for a longer period of time and has a darker color. A brown roux is cooked for the longest period of time and has the darkest color. The color of the roux will determine the color of the sauce.