Filé powder is made from dried sassafras leaves and used as a thickening agent. Originally used by the Choctaw Indians of the Gulf Coast to thicken soups, filé became a part of Cajun cooking. It is typically used to add a last bit of thickness and flavor to a gumbo. It is added to each person's bowl of gumbo right before eating, as it can become stringy and too thick if it is boiled.
The Choctaw Indians at first only crumbled the dried sassafras leaves into their soup, but with the introduction of enslaved Africans, the mortar and pestle became the preferred method of making filé powder.