Brown roux is a mixture of equal parts flour and fat, typically butter, cooked together until it reaches a deep brown color. This cooking process develops a rich, nutty flavor, making it a key ingredient in many dishes, especially in French cuisine. Brown roux is often used as a thickening agent in sauces, soups, and stews. It is a crucial component in dishes like gumbo and etouffee, where it adds both flavor and texture. The longer the roux is cooked, the darker and more flavorful it becomes, but it also loses some thickening power.