Turn on oven, set at 450 degrees. Wash and grease 3 medium potatoes. Bake 50 minutes, or until soft to the touch. Cut in halves, lengthwise, and scoop out centers. Save 4 half skins. Mash potatoes and add 1/2 cup Pet milk, 3 teaspoons water, 1 1/4 teaspoons salt and 1/8 teaspoon pepper. Beat until light and fluffy. Pile into potato skins. If desired, top with 1/4 cup grated American cheese. Return to oven and bake 15 minutes or until browned. Serves 4.