This is a modification of a recipe I found online somewhere, which is basically a riff on the regular 7 minute boiled frosting. It produces the best, fluffiest frosting ever, holds shape extremely well and takes color like nobody's business! This is my new go-to cupcake icing, for sure!
In a double boiler, or using a heat resistant glass mixing bowl over a pot of boiling water (it has to be a pretty tight fit, and the bottom of the bowl should not touch the water!) mix together the sugar, water, egg whites, cream of tartar and corn syrup. Use a hand mixer on slow speed and scrape bowl occasionally.
I normally start mixing before the water comes to a boil. Beat until all sugar is dissolved. Mixture will thicken and become pure white and foamy looking. Continue beating at medium speed until stiff peaks form.
Melt marshmallow chunks in the microwave. ( I use the "melt chocolate" setting on mine). Mix the melted marshmallows into the frosting and beat until all mixed in. Remove from heat.
You can pipe or spread this icing. Because it is super white, it takes color really well. You could also add flavour for extra pizzaz.