Melt in a saucepan on medium high heat 1/4 cup butter.
Add 1/4 cup flour.
Mix until combined.
Then add 2 cups of milk, stirring constantly. When it is thick and at a low boil start adding cubes of cheese. I always use 2 bricks of Extra Sharp Cheddar and cut it up into little cubes.

When all cheese is added and completely melted, pour it over your already cooked elbow noodles. I think I use the 8 oz. box, but I don't have a box of elbow noodles here to verify that. Sorry. Also, I never use the entire box of noodles, only because when you bake it you want it to be a little wet because it dries out a little. I would guess a small bowl of the noodles I don't end up using.

Then you cover it with extra sharp shredded cheddar and bake it on 350 for at least a half hour or more. I like the real crispy top so I bake ours a little longer.