Cook macaroni according to box, pour into colander and leave. DO NOT RINSE>.
Turn burner to med. Melt butter in pan, add flour and whisk together. Add milk and whisk constantly till warm and thickened. Remove from heat. Whisk in Velveeta, 1 cup cheddar and mozzarella, till melted and smooth.
Add macaroni to cheese mixture. Stir until well combined.
Heat oven to 350°F Pour mac and cheese into 2 qt casserole. Top with remaining cheese.
Bake for 20 minutes or till cheese on top is melted.