Which sauce is based on milk and used as a base for many others?

Béchamel is a classic white sauce made from a roux of butter and flour, combined with milk. It serves as a fundamental base for many other sauces, such as cheese sauce, creamy sauces, and gravies. Béchamel's creamy texture and flavor profile make it versatile in both savory and sweet applications, allowing chefs to create numerous derived sauces.

In contrast, Hollandaise, while an important sauce, is an emulsion made from egg yolks and butter, not based on milk. Tomato sauce is primarily made from tomatoes and is a foundational sauce in its own right, but again, it does not have a milk base. Espagnole, or brown sauce, is made from a brown roux, mirepoix, and stock and does not incorporate milk either. Béchamel's role in culinary foundations, particularly in French cuisine, makes it unique and essential for many dishes.