Cook macaroni according to package directions until al dente, then drain and set aside.

In the same pot over medium-low heat, melt butter and pour in milk, stirring until warm but not boiling.

Add garlic powder, mustard powder, salt, and pepper, then stir to combine.

Add shredded cheeses one handful at a time, stirring constantly until fully melted and smooth.

Return macaroni to the sauce, stir to coat evenly, and serve immediately.