Which method is used to make a sauce thickened with flour and butter?

The method used to make a sauce thickened with flour and butter is called a roux. A roux is a mixture of equal parts flour and fat, typically butter, that is cooked together to form a paste. This mixture serves as a thickening agent for sauces and soups. When the roux is combined with liquid, it helps create a smooth and creamy texture, which is ideal for various types of sauces, such as béchamel or gravy.

To make a roux, the flour is added to melted butter and cooked on low heat until it reaches a desired color, which can range from a pale blonde for light sauces to a darker brown for richer, more complex flavors. This cooking process helps to eliminate the raw taste of the flour and contributes depth to the final sauce.

The other methods listed have different purposes in cooking. Blanching involves briefly cooking food in boiling water and then placing it in ice water to stop the cooking process, primarily used for vegetables. Reducing refers to the technique of simmering a liquid to evaporate some of the water, concentrating flavors and thickening sauces but not specifically using a flour and butter mixture. Emulsifying is the process of combining two liquids that normally do not mix, such as oil