What is a roux?
A roux is a thickening agent made by heating equal parts starch and either fat or oil in a pan until a smooth paste is formed. Typically, vegetable oil, canola oil, lard or butter can be combined with a starch, like all-purpose white or wheat flour, to serve as a base for your saucy dish. During cooking, the flour absorbs moisture, leading to a sauce with a smooth consistency.
A roux can range from light to dark in color and darkens the longer it cooks. Typically, light colored roux is used to thicken dishes like soup or chowder, and is heated for a few minutes. Darker colored roux sauce is cooked longer and boasts a deeper flavor, which is ideal for dishes like seafood gumbo or gravy.