7-Minute Frosting

2 egg whites
1 cup granulated sugar
1/4 teaspoon cream of tartar
1/8 teaspoon salt
1/4 cup water
1 cup Marshmallow Cr?me
1 teaspoon vanilla extract

Combine all ingredients except vanilla extract in the top of a double boiler. Place over boiling water. Beat until soft peaks form. Remove from heat and beat until stiff. Beat in vanilla extract.