Boil sugar and water while stirring frequently until syrup reaches 235 degrees or syrup forms a soft ball in ice water. Remove from heat.
Break the marshmallows in pieces and to the hot syrup. DO NOT STIR. Let sit 1 -2 minutes. Pour slowly over the stiffly beaten egg whites, beating rapidly.
Continue beating frosting until it reaches desired consistency to spread. If it gets too thick to spread beat in a few drops of water.
Notes
Yield- Enough frosting to frost 2-3 dozen cupcakes.