Fluffy Marshmallow Icing
["1 c. sugar", "1/3 c. water", "1/4 tsp. cream of tartar", "2 egg whites (1/3 c.)", "8 soft marshmallows, quartered", "1 tsp. vanilla"]
["Combine sugar, water and cream of tartar in a saucepan.", "Boil rapidly until syrup spins a 6-inch to 8-inch thread (242\u00b0 on candy thermometer)."]
["sugar", "water", "cream of tartar", "egg whites", "marshmallows", "vanilla"]