This is the only one you need!
Preheat the over to 350°.
Cook pasta per package directions and drain. While it’s boiling, melt the butter in a heavy saucepan and then add the flour.
Stir butter and flour mixture continuously over medium heat for about 3-4 minutes–do not let it brown. Slowly add the hot milk, stirring to combine and remove any lumps. Add salt and pepper to taste.
Return pasta to pot and pour white sauce over it. Mix in about 8 oz. of shredded cheese and stir to combine.
Pour into a lightly greased 9×13″ dish and add the other 4 oz. of shredded cheese on top, if desired. Bake at 350° for 20-25 minutes and then broil until top is slightly golden and bubbling.