Cook macaroni according to package directions. In large saucepan, melt butter. Add onion and cook until tender. Stir in flour, salt. mustard, salt and pepper. All milk slowly, stirring constantly, and cook until sauce is thickened and bubbly. Add cheese and stir until melted. Combine cooked macaroni and cheese mixture and mix well. Pour into buttered casserole. (I use one that's about 12" square). Top with topping and bake in 375 oven for 20 25 minutes. To make topping: tear roll apart and use steel blade of food processor to chop into fine bread crumbs. Melt better in small saucepan then add crumbs and toss until covered with butter. Combine buttered crumbs with cheese and spread over casserole. I generally serve this with sauteed Kielbasa. Kraft's Macaroni and Cheese is great and I always have boxes in the cupboard as it's something my son can make in a hurry. However, "sure doesn't compare to Mom's!" As with many of my recipes, I evolved this from one I originally found on a macaroni box.