Cook macaroni, make a white sauce. I can't remember the exact measurments but this will work. You are making a rue. So one tablespoon butter, one plain four. Heat over medium heat in a heavy based pan. Constantly stir for a minute or two to cook out the taste of flour. Add milk (start with 1C and add more if you want a thinner sauce) Stir constantly, if it catches it will burn. Bring to a simmer and wait till it thickens. Add any flavour ie. cheese, vegies etc. Pour over macaroni top with cheese and place in oven until cheese is browned.
It sounds like alot of work but it doesnt take more than 7 mins really. Just make sure you keep stirring