Usually, it consists of half Gruyere and half Parmesan cheese, but you can create your own unique combinations.
Variations include additions of egg yolk and grated cheese.
This is a great example of how many different sauces you can make just changing the cheese you use.
The cheese you use will dictate the flavor of the sauce.
So if you refer to our wine and cheese chart, you can select the cheese that complements the wine you are serving and use that cheese in your sauce.