Heat butter in med saucepan on med heat. Whisk in flour; cook 2 min, stirring constntly. Gradually stir in milk; cook until mixture boils and thickens, stirring constanlty. Add Velveeta; cook 3 min or until melted, stirring frequently; Stir in macaroni.
spoon into 2qt cassorole spraying with cooking spray: Sprinkle with chedder cheese..