Heat oven to 350°. Mix together sugars, butter, egg yolks, water and vanilla. Add dry ingredients. Beat reserved egg whites until stiff; add to mixture. Pour mixture into a greased 9x13-inch baking pan. Bake for 30 to 40 minutes. Frosting: Cook sugars and cream to softball stage; add peanut butter and mix well. Allow cake to cool before frosting. Yields 12 servings.