Preheat oven to 350? F. Drop potatoes and salt into boiling water. Parboil for about 8 minutes. Drain well. Grease a 10 inch baking dish. Layer potatoes and onions in 3 layers, sprinkling each layer with flour and dotting with butter. Heat cream and season with salt, paprika and dry mustard. Pour over potatoes. Bake about 35 minutes, testing for doneness with a fork. ~~~~~