Heat The Oven To 400 Degrees F. Stir The Soup, Milk, Mustard, Pepper, Pasta And 1 1/2 Cups Of The Cheese In A 1 1/2-Quart Casserole. Bake For 20 Minutes Or Until It'S Hot And Bubbling. Stir The Mixture. Sprinkle With The Onions And Remaining Cheese. Bake For 1 Minute Or Until The Onions Are Golden.