Cook macaroni according to directions on package, about 10 to 15 minutes. Drain macaroni and put in a medium baking dish.
Now add Cheez Whiz and mix well till all is melted. Then add cheddar cheese a little at a time (saving 3/4 cup for top). Add milk mixing till all cheese is mixed in well. Put the remaining cheese on top of dish.
Bake in oven at 325 degrees F for 15 to 20 minutes or until all cheese is melted and light brown on top.