Wow, this started as a "what's in the cupboard" meal, and I'm already planning which parties I'll be making this for. I used butter instead of margarine and about 6-7- oz of Cheddar. I covered it with foil for 30 minutes, then removed the foil, sprinkled breadcrumbs on top, then baked it uncovered for another 30. It turned out nice and browned with a great crispy top. It wasn't super greasy like some other mac 'n' cheese recipes I've tried. Also added a couple dashes of nutmeg and garlic powder. Paired with a chianti and green beans, it made a great meal with lots of leftovers.