Cook pasta as directed on package. Drain well.
Stir milk gradually into Sauce Mix with whisk in small saucepan until well blended. Add butter. Stirring frequently, cook on medium heat until sauce comes to boil. Reduce heat and simmer 2 minutes, stirring occasionally. (Sauce will thicken upon standing.)
Serve over pasta. Sprinkle with grated Parmesan cheese, if desired.