From the Moosewood Restaurant Low-Fat Favorites cookbook, which I suggest you check out in person because it is very awesome.
I also threw some fresh spinach in here, just into the mixture before the breadcrumb step, and it turned out really well.
1 1/2 c 1% cottage cheese
1 1/2 c skim milk or buttermilk
1 t dried mustard or 1 T prepared mustard
pinch of cayenne (or more)
1/4 t nutmeg
1/2 t salt
1/4 t ground black pepper
1/4 c grated onions
1 c grated sharp cheddar (4 oz.)
1/2 lb. uncooked elbow macaroni (or other tubular pasta)
2 T finely grated Pecorino or Parmesan cheese
1/4 c bread crumbs
Preheat oven to 375. Prepare square baking pan with a light spray of oil.
In a blender, combine cottage cheese, milk, mustard, cayenne, nutmeg, salt and pepper and puree until smooth. In a large bowl (actually, I did this right in the baking dish), combine pureed mixture with the onions, cheddar and uncooked macaroni. Stir well. Pour macaroni and cheese mixture into the baking pan. Combine the grated Pecoino or Parmesan and bread crumbs and sprinkle over top.
Bake about 45 minutes, until topping is browned and the center is firm.