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 process involves creating a roux by cooking equal parts of butter and flour, then gradually whisking in milk until the sauce thickens. This versatile sauce is often used in recipes like lasagna, macaroni and cheese, and croque monsieur. It can be flavored with ingredients such as nutmeg, cheese, or herbs to enhance its taste, making it a staple in both savory and creamy dishes.