I've always liked this recipe:

http://www.food.com/recipe/ronzoni-m...-cheese-358936

I use 2 1/2 cups of extra sharp cheddar and leave out the American cheese. I substitute 1 teaspoon onion powder for the minced onion.

Don't leave out the dry mustard--it gives the dish just a little bite. (I have a friend who seems to have a phobia about this ingredient. I have no idea why, since she loves mustard!)