Bring large pot of salted water to boiling. Add macaroni; cook following package directions. Drain.
Meanwhile, in medium-size saucepan, melt butter over medium-low heat. Add onion and garlic; cook, stirring occasionally, until softened, about 7 minutes. Add macaroni, pasteurized cheese, Parmesan and milk; cook, stirring, until cheeses are melted and smooth. Season with pepper sauce.