Which of the following is NOT one of the five mother sauces in classical French cuisine?

The concept of the mother sauces in classical French cuisine is foundational in culinary training. These sauces serve as the basis for many other sauces and are traditionally recognized as a group of five: Béchamel, Espagnole, Velouté, Hollandaise, and Tomato. Among the options given, Béchamel, Espagnole, and Hollandaise are indeed classified as mother sauces.

Roux, on the other hand, is not a mother sauce. Rather, it is a thickening agent made from equal parts flour and fat, commonly used in cooking to create the base of several sauces, including some of the mother sauces like Béchamel and Velouté. The distinction here is essential: while mother sauces are categories of sauces from which many derivatives are made, roux is a technique or mixture employed in the preparation of those sauces. Thus, recognizing the definition and role of each component in classical French cooking clarifies the misplacement of roux in the list of mother sauces.