Melt the salted butter in a saucepan over medium-low heat. Stay close so it does not brown.
Add the heavy whipping cream and whisk until it reaches a gentle rolling boil.
Add the Parmesan cheese and whisk consistently for about 10 minutes, until the cheese has melted and the sauce is smooth and slightly thickened.
Remove from heat and let the sauce stand for 3 to 5 minutes so it tightens up.
Pour over cooked, drained pasta and toss to coat. Serve immediately.
Notes
Use heavy whipping cream, not milk or half-and-half, so the sauce thickens and stays smooth. Skip powdered Parmesan because it can make the sauce grainy. Have the pasta ready before starting because the sauce comes together quickly. Let the sauce stand for a few minutes off heat before judging the thickness.