Cook the Macaroni: – Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to the package instructions until al dente. Drain and set aside. Prepare the Cheese Sauce: – In a saucepan, melt 1/4 cup of butter or margarine over medium heat. Stir in enough flour to make a roux. Add milk to roux slowly, stirring constantly. Stir in cheeses, and cook over low heat until cheese is melted and the sauce is a little thick. Put macaroni in large casserole dish, and pour sauce over macaroni. Stir well.