Remove the leaves from the sassafras tree during early fall, before the leaves change colors.
Wash the leaves to remove any dirt or contamination.
Bundle the stems together, tie, and hang the leaves in a cool dark place. Do not disturb until the leaves are dry and break easily.
Break the stems off of the leaves, and remove any thick veins running throughout the leaves
Break apart the leaves and grind in a food mill, coffee or spice grinder, blender or food processor. Continue to grind until the leaves are reduced to a fine powder.
Place the filé powder into a flour sifter and sift until all the fine particles are out. Discard what is left in the sifter.
Put the filé powder into a jar with a tightly sealed lid. Label with the date and name. Store in a cool, dark cabinet or the refrigerator.
Add a small amount to a dish at the last minute, or after cooking. Filé powder will become gummy if overused or overcooked.