Roux

The fourth method for getting starch into a sauce, and one that has been developed into a minor art of its own, is to preheat the starch separately in fat to make what the French call a roux, from the word for “red.” The basic principle works with any form of starch and any fat or oil. In the traditional French system, the cook carefully heats equal weights of flour and butter in a pan to one of three consecutive endpoints: the mixture has had the moisture cooked out of it, but the flour remains white; the flour develops a light yellow color; or the flour develops a distinctly brown color.