A foundation of French cuisine, roux is a mix of fat and flour. Butter is more traditional, but oil works, especially when you don't want a rich flavor. Roux is a thickener, an ingredient in gumbo and etoufee and the foundation for bechamel -- white sauce. Bechamel in turn is a foundation for white sauces, souffles, mac and cheese and other dishes. For a proper roux, use the right ratio of flour to oil.
Ready, Set, Roux
To make a roux, the correct ratio of flour to oil is equal parts. If you use 1/2 cup of flour, use 1/2 cup of oil. Heat the oil in a heavy-bottomed pan over medium heat until it develops a watery consistency. Then, sprinkle flour evenly into the pan. Whisk the ingredients together continuously for about seven minutes, until a light blond color develops. The roux needs to be cooked enough to get rid of the raw flour taste. Clumps form initially, but the roux will become smooth if you used the right ratio.
Use the Roux
Use a blond roux for bechamel and gravies. To make bechamel, stir room temperature or warm milk into the roux; the more you use, the thinner the sauce. From there, add herbs, spices or grated cheese for a sauce. For a Cajun dish, cook it longer, still whisking continuously, until a chocolatey color develops. It's a less effective thickener at this point, but it adds color and flavor to your final dish.