Which ingredient is NOT included in the Mornay Sauce recipe?

In the traditional Mornay Sauce recipe, Gruyère cheese, plain flour, and butter are essential components. Mornay Sauce is a béchamel sauce enriched with cheese, most commonly Gruyère or sometimes Parmesan. The process typically begins by making a roux with equal parts of butter and flour, which forms the base of the sauce. Milk or cream is then added to create a velvety texture, after which the cheese is melted into the mixture, creating the rich and creamy sauce that is characteristic of Mornay.

Although heavy cream can enhance the creaminess of a sauce, it is not a standard ingredient for Mornay Sauce. Instead, milk is traditionally used when preparing the béchamel base. This adherence to using milk aligns with classical cooking techniques and the fundamental recipe for Mornay, thereby omitting heavy cream as an essential component.

In summary, the reason heavy cream is not included is due to the traditional preparation methods and the standard ingredients that define Mornay Sauce, relying primarily on milk for its characteristic texture and flavor.