ADD macaroni to boiling water; COOK until barely tender; DRAIN well.

Meanwhile, in a medium sauce pan, MELT the butter; ADD the flour; COOK, STIRRING constantly, until the mixture thickens.

Gradually ADD the milk, STIRRING constantly, until the white sauce bubbles and thickens; Let it COOK gently for a minute or two, STIRRING frequently.

TURN off heat; STIR in the cheese, letting it MELT into the sauce.

COMBINE macaroni with cheese mixture; SPOON into buttered, shallow baking dish.

BAKE in a preheated 425 F oven until the top is browned, about 20-30 minutes.