Place the butter in a medium pot over medium heat and melt. Stir in flour until well-blended and cook for about a minute. Add milk and mix in well. Bring to a bubble just before a boil. Add cheese and stir until completely melted.
While the sauce is cooking, boil macaroni in lightly salted water for 2 minutes LESS than the box recommends. Strain and place in sauce, mix together well, season with salt to taste.