One of the key ingredients to making file gumbo (as opposed to okra gumbo, in which okra acts as the thickener), this seasoning is made from the ground, dried leaves of the sassafras tree. Indians from the Louisiana Bayou were the first to begin using it. Its primary purpose is to thicken and flavor gumbos and other Creole specialties. This seasoning must be added to the sauce after it has been removed from heat otherwise it gets much too thick. Look for it in your grocer’s spices section.