The food item you are referring to is a “white sauce,” also known as a “béchamel sauce.” It is a basic sauce that is made using a white roux, which is a mixture of butter and flour that is not browned. This distinguishes it from brown sauces, which are made using a brown roux. While many recipes in the United States use milk to make white sauce, it can also be made using stock. Béchamel sauce is a staple in French cuisine and is often used as a base for other sauces, such as cheese sauce or Mornay sauce. It can also be used as a topping for vegetables, pasta, or other dishes.