Place 1 T. of the butter in the pan; add the garlic, onion and mushrooms. Cook until the vegetables begin to soften, about seven minutes; stirring as needed.
Add the cheeses and turn heat to low. Stir in the rest of the butter, heavy cream, chicken and nutmeg. Simmer for about five more minutes or until all ingredients are hot and the sauce is slightly thickened. Add salt and pepper to taste and serve over the pasta. Enjoy!