In a medium saucepan over medium-high heat, add the butter and cream cheese, stir until melted. Whisk in heavy cream, milk, and garlic powder until smooth.
Remove from the heat and stir in parmesan cheese, black pepper, and salt.
Toss with your favorite pasta.
Notes
Tips for Storing
Refrigerator: Store the sauce on its own (without pasta) in an airtight container for up to 4 days. The cream cheese gives it better fridge stability than a classic Alfredo, which tends to seize up almost immediately.
Reheating: The trick is low and slow. Reheat over low heat in a saucepan with a splash of milk or cream, whisking constantly. Microwave only as a last resort, and stir every 30 seconds. A high-heat reheat is what breaks a cream sauce nearly every time.
Freezing: I don't recommend it. Cream-based sauces don't freeze and thaw well. They separate into a watery layer and a fatty layer no amount of whisking truly fixes. If you have to, freeze in small portions and accept that the texture won't be quite the same.
Make-ahead for entertaining: Make the sauce up to 4 hours ahead and hold it warm in a low oven (180°F) covered, with a piece of parchment pressed directly onto the surface to keep a skin from forming. Reheat gently with a splash of milk just before serving.