White Mountain Frosting is really just an Italian Meringue. The technique is fairly straight forward, beat egg whites until stiff with cream of tartar. Adding a hot sugar syrup to the mixture, which cooks the whites, resulting in a lovely stable marshmallow cream frosting. Here you go Lisa and Mariam...the recipe!
If you per chance have left over frosting...you can pipe (or drop by the spoonful) onto a baking sheet lined with parchment or a silpat, bake at 225 degrees for 2 hours, then let cool in the oven for another 3 hours--Presto Magico...Meringue Cookies!
White Mountain Frosting (adapted from Cooking Light)
4 large egg whites
1/4 tsp cream of tartar
Dash of salt
1 cup sugar
1/4 cup water
1 tsp vanilla extract
(other extracts such as lemon or coconut can also be used, decrease vanilla to 1/2 tsp and use 1/2 tsp of your desire extract)
Place egg whites, cream of tartar and salt in the bowl of a stand mixer or other large mixing bowl--taking care NOT to use plastic. Beat with a mixer until stiff peaks form. Combine sugar and water in a saucepan, bring to a boil. Cook, without stirring, until a candy thermometer registers 250 degrees. Pour hot syrup in a thin stream over egg whites, beating at high speed. Stir in extract.