Kudzu powder by John Spottiswood.

This thickener is made from the tuber of the kudzu, the obnoxious vine that was imported from Japan a number of years ago and is now growing out of control all over the South. It's very expensive, and the main reason to buy it is for its reputed medicinal benefits. It comes in small chunks. To thicken a liquid, crush the chunks into a powder, mix them with an equal amount of cold water, then stir the mixture into the hot liquid and simmer for a few minutes until the sauce is thickened. Look for kudzu in health food stores.