Brown Sugar Marshmallow Frosting

2 cups brown sugar, firmly packed
1 cup granulated sugar
3/4 cup water
1/2 teaspoon vanilla extract
5 marshmallows
2 egg whites

Cook sugar and water over low heat until it spins a thread. Add vanilla extract and marshmallows. Beat until marshmallows are dissolved. Pour gradually onto the stiffly beaten whites, beating constantly.