Melt the butter in medium heat in a medium saucepan.
Add the heavy cream and whip. Boil until it begins to simmer, but not boil.
Little by little, add Parmesan cheese and keep stirring until it is completely melted and smooth.
Salt, black pepper, and nutmeg may be used.
Keep stirring until the consistency of the sauce reaches the desired size (approximately 5-7 mins).
Take out of the heat and allow to rest 2 minutes then serve.
It can be served over any dish of your choice, which is keto-friendly, although garnished with chopped parsley, which is optional.