The different varieties of gruyere sauce are distinguished from one another primarily by the flavor ingredients that are added to a basic white cheese sauce. Gruyere has a subtle flavor profile, and can be mixed successfully with a wide variety of other flavors, including spices, several types of alcohol, and other cheeses. Although not technically a sauce, cheese fondue is also often built using gruyere cheese.
Gruyere cheese is a mild, firm white cheese. It has a distinctive flavor but not an especially strong one. This flavor profile means that it can be successfully blended with a wide variety of other ingredients without producing unpleasant flavors.
In most cases, a gruyere sauce is built on a simple bechamel sauce. This simplest of all sauces in traditional French cooking consists of a roux made from butter, flour, and scalded milk. The roux and milk are combined to produce a sauce that is both rich and creamy, thanks to the butter, milk, and the starch from the flour.
Cheese is often added to a bechamel sauce, and a gruyere sauce is one of the most common types of sauce produced in this fashion. Mornay sauce is created by adding gruyere cheese together with some mixture of other white cheeses to the basic white sauce. The resulting sauce is even richer than a simple white sauce, and is infused with the flavors of the cheeses. This sauce is often modified by adding spices with fairly mild flavors, such as white pepper or various herbs.
Meals with gruyere sauce may also make use of sauces built on a stock base. Gruyere melts easily and quickly and can be melted into a chicken or fish stock base to add richness and flavor to a sauce. In this type of application, gruyere sauce is often flavored with spices appropriate for the protein that the sauce will be served with. Pepper and paprika, for example, could be added to a gruyere sauce built on a chicken stock base for use over roasted chicken.
Another common example of a gruyere sauce, or something very much akin to a sauce, is cheese fondue. This type of fondue is prepared by slowly melting cheese, typically gruyere and some other light cheese, into a warm liquid base consisting of white wine and sometimes kirsch. Mild spices such as mustard are then added, and bread or vegetables are dipped into the fondue, which is kept warm and smooth while it is being served.