Heat oven to 350. Spray a lg casserole dish w/ cooking spray. Cook macaroni as directed, drain. In lg bowl, combine soup, sour cream, milk, mustard, salt and pepper.
In saucepan, mely butter over medium heat. Add cheese, stir until cheese is melted. Reserve 1/4 cup cheese. Pour remaining cheese sauce over macaroni, mix well. Pour the soup mix over macaroni and mix.
Cut each bisciut into quarteres and fold into macaroni mix. Spoon everything into casserole dish. Cover, bake 25 mins. Sprinkle w/ reserved cheese. Bake 20 mins more.