Heat the butter in a small saucepan over medium heat; stir in the garlic. Cook for 30 seconds until fragrant.
Whisk in the flour and stir to make a roux.
Add the milk, onion powder, salt, pepper, and Parmesan cheese.
Cook and whisk continuously for about 5 minutes until the cheese is melted and the sauce has thickened slightly. Add more milk if the sauce is too thick.
Remove from heat and enjoy on pizza or as a dipping sauce for breadsticks.
