Melt butter in a non-stick saucepan over medium heat; melt cream cheese and garlic powder in butter, whisking Pour in milk, a little at a time, whisking to smooth out lumps. Stir in Parmesan cheese and pepper until smooth.

Remove from heat when sauce reaches a creamy and thick consistency, about 5 minutes. This sauce will thicken rapidly as it cooks - thin with additional milk if cooked for too long.