Meanwhile, in a small saucepan, bring the milk to a bare simmer over medium heat. In a medium bowl, whisk the egg briefly to break it up. Temper the egg by drizzling 1/2 cup of the warm milk in while whisking until incorporated. (This will prevent the egg from scrambling.) Mix the tempered egg and the remaining warm milk into the macaroni and stir well until everything is evenly coated.