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 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.