Which component combination primarily builds a roux?

A roux is a mixture of fat and flour that is used as a thickening agent in various sauces and dishes. The combination of equal parts fat, typically butter, and flour is heated together to create this foundational element in cooking. During the cooking process, the fat coats the flour, preventing it from clumping and allowing it to be combined with liquids without forming lumps.

This mixture is cooked for a certain period, depending on the desired flavor and color—ranging from a white roux to a darker brown roux. The type of fat can vary, but commonly used fats include butter, oil, or lard. Once the roux is properly prepared, it can be gradually blended into a liquid, such as stock or milk, to create creamy sauces like béchamel or gravies.

The other options do not represent the correct components for making a roux. Water does not contribute the necessary fat content required for this purpose, and milk contains additional liquids that would not create the characteristic thickening effect. Hence, the primary components for building a roux are equal parts fat and flour.