Chicory describes a group of bitter greens in the sunflower family, the likes of which, those of us who love to cook are very familiar: Belgian Endive (Witloof), Curly Endive (or Frisee), Escarole, and Raddichio. The Chicory we're interested in here, the one used for extending coffee, Cichorium Intybus, is a perennial herb, which grows wild in parts of the country, and has flowers that are usually blue. It has a root resembling a white carrot, getting as large as 2" at the top and 14" long. Before Chicory root is used for coffee, it is sliced, kiln-dried, roasted with a little oil until dark, and ground to desired fineness. The addition of Chicory to Coffee makes it stonger, thicker, and slightly bitter. I think it adds an almost unsweetened Chocolate flavor and consistency.
I've read different versions of who first starting using Chicory to extend coffee, here is what I've heard. The first known use was in the 1600's, some say of Dutch origin (as am I), some say French, some say Chicory was first used to extend coffee for Napoleon's troops. As far as New Orleans and the United States is concerned, maybe it started during the Civil War due to Naval blockades, which blocked the import of coffee. Maybe the French brought it with them. Who knows? One thing I do know is that Chicory makes New Orleans Coffee distinctive from all other Coffees in the States, and possibly the world.
Certain grocery stores in my area sell Ground Roasted Chicory on its own for extending coffee, and French Market brand Coffee with Chicory, which is what Commander's Palace uses, is available just about anywhere. If you live in the Detroit area, Rafal Spice Company in Eastern Market sells a whole bean, New Orleans Style Coffee with Chicory that is very good.