STIR together milk and cornstarch in a small bowl until cornstarch is dissolved (tilt bowl to make sure no lumps remain).
MICROWAVE until boiling and thickened, about 40 seconds. Whisk in cheese until well combined.
RETURN to microwave for 10 second intervals, whisking each time, or just until cheese is melted and blended.
SERVE with veggies and pretzel sticks for dunking.