White sauce is the most basic of sauces. Often called "béchamel" by the French.
In French cooking, traditional white sauces are one of two types: those made with hot milk added to a white roux (such as Béchamel sauce or Mornay sauce) or sauces made with hot broth or stock added to a white roux (such as Velouté sauce). A roux is a combination of flour and butter that are cooked together to be used as a thickening agent for the sauce. The roux may be referred to as a white, blonde or brown roux, depending on the amount of cooking time allowed for the flour or mixture that increasingly darkens the roux as it cooks. The hot milk or stock is stirred into the roux to create a thick sauce that may be seasoned with herbs and spices.