Roux is made by cooking equal parts flour and fat together until the raw flavor of the flour cooks out and the roux has achieved the desired color. Butter is the most commonly used fat, but you can also make roux with oil, bacon grease, or other rendered fats.
If you’re cooking and storing a batch of roux for future use, use clarified butter as it will harden when refrigerated, trapping the flour in suspension. This suspension helps to prevent lumps when the roux is whisked into a sauce or soup. Having a well-made roux on hand will make it easy to use this marvelous thickener in everyday cooking.
There are four varieties of roux: white, blond, brown, and dark brown. The different colors are a result of how long the roux is cooked; white is cooked for the shortest time, while dark brown cooks the longest. White and blond roux are the most common, used to thicken sauces, soups, and chowders. Brown and dark brown roux have more flavor, but less thickening power than white or blond roux. Dark roux are primarily used in Cajun and Creole dishes, most notably gumbo and jambalaya.