Two ingredients--flour and oil--make roux. The slow-cooked blend contributes a rich depth of flavor to Creole and Cajun cookery and is the heart of every real gumbo. Plan to spend from 30 to 40 minutes whisking the precious thickener depending on the size of your pot, the amount of oil, and the temperature. You can't rush that smoky, nutty flavor. If the heat is too high, the roux will burn, then you'll have to throw it away and start over.
Store roux in an airtight container in the refrigerator for up to two weeks. Any time you want gumbo, you're ahead of the game.