1 1/2 cups sugar
2 large egg whites
1/3 cup water
2 teaspoons light corn syrup
1/4 teaspoon cream of tartar
1 teaspoon vanilla extract
Whisk sugar, egg whites, 1/3 cup water, light corn syrup, and cream of tartar in large metal bowl to blend.
Set bowl over saucepan of barely simmering water (do not allow bottom of bowl to touch simmering water).
Using handheld electric mixer, beat on medium speed until mixture resembles soft marshmallow fluff, about 4 minutes.
Increase mixer speed to high and beat until mixture is very thick, about 3 minutes longer.
Remove bowl from over simmering water.
Add vanilla extract and continue beating until marshmallow frosting is completely cool, about 5 minutes longer.
Put the frosting in a ziploc bag and snip the end to pipe onto the cupcakes. Sprinkle with leftover coconut.