Old Fashioned Marshmallow Icing
Light meringue-based icing with a marshmallow-like quality.

Bring sugar, corn syrup and water to boil. When this is just boiling, start whipping the whites in a stand up mixer. When it's soft peaks, add a pinch of salt and the vanilla. When the syrup reaches 112°C (234°F), reduce the speed of the whites (which should be peaked now) and slowly pour it into the whipped whites in a steady stream. Continue beating for a few minutes, or until the temperature has been reduced to warm. When no longer hot (but still slightly warm), use to frost the cake.

Note: the longer it is whipped, the stiffer the meringue becomes but the less time you have to work with it. Always work with it slightly warm because the icing sets up fairly quickly.