Easy Alfredo Sauce

1/2 cup butter
1 (8 ounce) package cream cheese (or neufchatel cheese)
2 teaspoons garlic powder
2 cups milk
6 ounces grated Parmesan cheese
1/8 teaspoon ground black pepper

Melt butter in a medium, non-stick saucepan over medium heat. Add cream cheese and garlic powder, stirring with wire whisk until smooth. Add milk, a little at a time, whisking to smooth out lumps. Stir in Parmesan and pepper. Remove from heat when sauce reaches desired consistency. Sauce will thicken rapidly, thin with milk if cooked too long. Add mushrooms and/or cooked boneless chicken breast if desired. Serve over pasta.