Bring a large pot of salted water to a boil and cook the pasta according to package directions, just until al dente. (Pasta will continue to cook when added to the sauce.)
In a large saucepan, melt the butter over medium heat.
Whisk in the cream and half and half. Heat the cream just to a simmer. Turn the heat off and whisk in the lemon juice and zest.
Add 1 1/2 cups of cheese and stir until smooth. Stir in the nutmeg. Season with salt and pepper to taste.
Add the cooked pasta to the sauce and the remaining cheese. Toss to coat until the sauce begins to thicken.
Sprinkle with fresh parsley, if desired. Serve immediately.
Video
Notes
Sauce can be made up to 24 hours in advance. Store in an airtight container in the refrigerator. Heat the sauce slowly over low heat stirring frequently to avoid separation.