A roux is a mixture of fat and flour that is slowly cooked over low heat. It is then used to thicken mixtures like sauces and soups. There are three basic types of roux. White roux is made from butter and cooked only until it begins to turn beige. Blond roux is also made from butter, but it is cooked longer, until it begins to turn golden. Brown roux has a fuller flavor and made using butter, pork, or beef fats or other drippings and cooked until is a deep golden brown. It is used to thicken dark, rich soups or sauces.

Cajun or creole dishes typically use a roux made with lard and are cooked until it is a dark brown, for almost an hour. This is a key ingredient in classic gumbo dishes.