Melt butter in a deep skillet over low.
Whisk in flour and cook for two minutes.
Gradually add milk and raise heat to bring mixture to a boil. Stir constantly.
Once it boils, lower to a simmer for 5 minutes to thicken it.
Whisk in cheese and once smooth add the pasta.
Pour into a greased casserole dish.
Sprinkle on extra cheese if desired and bake at 350 for 15-20 minutes.