Prepare the elbow macaroni according to package directions.
Meanwhile, melt the butter in a small saucepan over medium high heat. Stir in the flour until a cream colored paste forms. Then pour in the milk and stir constantly until this comes to a hard boil, then stir for 1 more minute. Add cheeses gradually to melt and create creamy cheese sauce.
Drain macaroni and add to cheese sauce. Pour into lightly greased casserole dish.
Bake at 350 degrees F (175 degrees C) for 35 to 45 minutes.