in 2 qt microwavable dish melt butter (1 min) add flour, salt & pepper, whisk till smooth, add milk, micro 2:30 minutes, stir, micro 2:30 minutes, stir, micro 2 more minutes, stir til smooth, add cheese micro 1 minute, stir til smooth, add sour cream (optional), add cooked mac & stir. bake (in regular oven) 20-25 minutes @ 350.