To make it, you add a sugar syrup to stiffly beaten egg white.It ends up fluffy and white.
It is practically fat-free, and less sweet than many other frostings
It is best served in a day or two; it may start weeping after that, particularly in humid weather.
The recipe appeared in Betty Crocker cookbooks, from at least 1955 onwards.
Variations:
1. Orange or lemon juice can be swapped for the water, orange or lemon zest can be added
2. Maple Mountain Frosting: swap brown sugar in for the white sugar, use maple flavouring instead of vanilla
Literature & Lore
White Mountain Frosting — Ingredients —
(a) one cup sugar, one-eighth teaspoon cream of tartar;
(b) one-third cup hot water
(c) white of one egg beaten until stiff,
(d) one-half teaspoon flavoring and one-half teaspoon baking powder.
Mix (a) thoroughly; add (b), pouring gently around the edges of the saucepan. Bring to the boiling point and boil until the syrup is thick. Add half to the stiffly beaten egg whites. Let the rest of syrup boil until it hairs. Add to first mixture. Beat until cool and add (d).” — Household Hints column. Madison, Wisconsin: The Capital Times. Friday afternoon, 27 April 1923. Page 14.
“1. Cooked Frostings — (a) The so-called boiled frosting — a sugar and water syrup poured and beaten into stiffly beaten egg whites; the White Mountain frosting (the same but with a larger proportion of egg white); and the seven minute frosting, for which all ingredients are put together in the double boiler, and cooked under constant beating.” — Caldwell, Katherine. The National Cooking School Series: Lesson 10. St Petersburg, Florida: The Independent. Tuesday, 12 February 1935
Sources
Author unknown. ‘Betty’ has classic frosting recipe. Everett, Washington State: The Daily Herald. 22 June 2009.
Baggett, Nancy. White Mountain Frosting in “The All-American Dessert Book.” Houghton Mifflin Harcourt, 2005. Page 144.