Béchamel sauce, also known as white sauce, is a fundamental component in many cuisines. This classic French mother sauce is made by whisking milk into a butter-flour roux. The thickness of the sauce depends on the ratio of flour and butter to milk. To make this sauce, start by melting butter in a saucepan over medium heat. Add an equal amount of flour to create a roux, cooking for a few minutes until it smells nutty. Gradually whisk in warm milk, stirring constantly to prevent lumps. Simmer gently until the sauce thickens to your desired consistency. Season with salt, white pepper, and a pinch of nutmeg for traditional flavor. This versatile sauce can be used as a base for many dishes, including lasagna, gratins, and creamy pasta sauces.