It's Filé Day
here in Louisiana, about the only place where that herb is routinely used in cooking. Filé is made by drying and crushing the leaves of the sassafras tree into a powder. Sassafras is a smallish tree that grows in the shady woods throughout the South. The leaves are unusual in having three distinct shapes, mixed uniformly throughout the tree. Some are leaf-like pointed ovals, some look like mittens, and others look like mittens with thumbs on both sides.
The one and only use for filé in the kitchen is a big one in these parts: making gumbo. It's usually a gumbo made with something like chicken or sausage. (I personally think it doesn't belong in seafood gumbo.) Some chefs add it during the cooking process as a thickener, but it has a bitterness when used that way. I think the aroma is better than the flavor, and so I dust it on the top of the gumbo at the table. I've tried using fresh sassafras leaves in gumbo, but that doesn't do a thing. Apparently the drying process is necessary for the aroma to emerge.
The name "filé" is derived from French, in which it translates as "string" or "line." When filé is stirred into a liquid, it forms a sort of string until it gets fully soaked. Filé's dirty secret is that parts of the sassafras tree have been found to be carcinogenic--notably the roots, which were once the source of flavoring (and the name) for root beer. Products containing the problematic substance are banned. However, little if any of that is in the leaves, and apparently the small amount of filé you ingest in gumbo isn't enough to hurt you. Although who knows?
You can make your own file. I've found a very thorough explanation of how to do so, along with pictures of sassafras leaves, at this web site.