Béchamel sauce is a classic white sauce made from a simple mixture of butter, flour, and milk. It is one of the five mother sauces in French cuisine and serves as a base for many other sauces and dishes. The sauce is typically thickened by cooking equal parts of butter and flour together, known as a roux, before gradually whisking in milk until smooth and creamy. This versatile sauce is often used in dishes like lasagna, macaroni and cheese, and croque monsieur. It can be flavored with various ingredients, such as cheese, nutmeg, or herbs, to enhance its taste and complement different recipes.