Roux

Combine oil and flour in heavy pot, preferably cast-iron. Cook mixture over low heat; stir constantly, until a rich caramel color is reached.

When desired color is obtained, add chopped seasoning (onion, bell pepper and celery) in order to lower temperature and keep roux from burning.

Continue to stir.

Always add hot water or liquid to roux.

Cold water will cause roux to curdle and flour and oil to separate.