Cajun and Creole recipes invariably begin with the words "make a roux". A roux is a simple mixture of flour and fat, used to thicken and flavor sauces in French and French-inspired dishes. By definition, a roux can be any color from white to brown. However, in South Louisiana, dishes like gumbo, shrimp stew and fricassee use a carefully prepared dark roux to add the rich, toasted flavor for which this regional cuisine is famous. Made properly, a dark roux will never leave a floury-tasting sauce or broth.
Place 1 cup vegetable oil and 1 1/3 cup granulated flour in a heavy saucepan. Place saucepan over medium-high heat. Whisk oil and flour to combine. Continue whisking for 1 minute.
Reduce heat to medium-low. Set aside whisk. Using a long-handled wooden spoon, stir flour and oil mixture continuously. Alternate between a circular and s-shaped stirring pattern, making sure to scrape the bottom of the saucepan while stirring.
Cook the roux, stirring constantly, for 15 to 20 minutes. Roux should be rich, red-brown color. When roux reaches the proper color, turn off the heat. Carefully add the chopped onions to the mixture. This will flavor and temper the roux. Carefully stir the mixture a few more times. When onions stop sizzling, the roux is ready to be added to your favorite recipe. Or, spoon roux into a heat-safe dish. When completely cooled, roux can be frozen in resealable plastic bags for later use.