This reply may be a bit late in the game…However, this is traditionally called a Seven-Minute Frosting (basically, because it takes about 7 minutes to make when you start to whip it over the double boiler).
I like this frosting, but the traditional version tends to be overly sweet and quite sticky (i.e hard to work with).
Last year, Cook’s Illustrated published a remade version that not only is less intensely sweet but is more stable and holds up for 3-4 days (twice as long as the traditional version. The CI version is also much easier to make as you don’t have to whip it over a double boiler (which is very tiring to the arm), just heat to to 160 while stirring with a spatula and then whip on the stand mixer.
Here’s the recipe:
4 large egg whites
14 oz. sugar
½ c. water
2 TBS. lemon juice
2 TBS. light corn syrup
1. Combine all ingredients in the stainless steel bowl of an electric mixer. Place bowl over hot water bath with barely simmering water.
2. Stir constantly until the mixture reaches 160 degrees, 5-10 minutes.
3. Put the bowl on the mixer machine and whip with wire whip on medium speed until stiff peaks form and the mixture has cooled to room temperature, about 5 minutes.
This icing is just lovely on a lemon layer cake (which is my all time favorite cake, btw), and this recipe was published with CI’s remade version of old-fashioned lemon layer cake (excellent recipe, and the lemon curd recipe with it is the best I’ve ever used as a cake filling).