Put the oil and flour in a cast-iron or enameled cast-iron pot over medium heat. Stir slowly and constantly. After 5 minutes, the mixture will begin to foam. This foaming may continue for several minutes. The roux will begin to darken as it cooks and will have a nutty aroma. For a blond roux, cook for 10 to 15 minutes. For a medium brown roux, cook for 30 to 35 minutes. For a dark brown roux, cook for 40 minutes.
When finished, roux can be cooled, then stored for 1 month in an airtight container in the refrigerator. When it cools, the roux will separate. Before using, stir to blend and bring the roux to room temperature.
Yield: 2 cups