Imagine a soft white layer of marshmallow over a cake. Its sweet, but not too sweet. Its light, but still satisfying. It tastes absolutely delicious when paired with chocolate cake. That's what you will get with marshmallow frosting, also known as Italian meringue.
As an added bonus, this is one of those recipes where you get to bring out the candy thermometer.
(1) Pour the sugar and water into a medium saucepan. On medium heat, bring the sugar and water mixture up to 245 degrees Fahrenheit. Do not stir, as this might cause crystallization.
(2) While you are waiting for the sugar to reach the right temperature, add the egg whites to a mixer, and start whisking. You want to bring the egg whites to the point where they form soft peaks.
(3) Very carefully remove the hot sugar from the stove, and slowly pour it into the fluffy egg whites, while still beating. You do not want to spill any of the hot sugar - it will burn!
(4) Once all the sugar is added, continue beating the frosting until it has cooled; it should take about seven minutes. The outside of the bowl will gradually cool down, and the frosting will double in volume.
(5) The frosting is done once it is cool, and has achieved a fluffy and glossy appearance.
(6) This recipe makes enough frosting for a two layer 6" cake, and should be more than adequate for a one layer 9" cake.
My family is gluten free for health reasons. And good news: this marshmallow frosting is entirely gluten free! No substitutions, no fuss, its just sugar, water, and egg whites by design.
Its also dairy free, which is what drew me to trying Italian meringue a few years ago. Before I discovered this pillowy delight, I always used buttercream on my cakes. But then I had to be dairy free for about six months for the sake of my baby daughter (milk protein intolerance; there were a lot of colicky nights). The combination of dairy and gluten free is pretty rough. But the good news is: this marshmallow frosting is naturally dairy free and gluten free!
Marshmallow frosting holds together nicely, and sticks to a cake. But it does not do well as a filling between layers. The weight of a cake easily pushes it out from between cake layers, leaving you with only a tiny coating. That is a significant disadvantage compared to buttercream.
There are a few ways to work around this.
One is simply to resign yourself to having a smaller cake. Maybe just two layers, with a light layer of filling in between each. Marshmallow frosting works fine for this.
Another is to provide another sort of structure to keep your layers separate. I have used fruit - specifically blackberries - secured with toothpicks for this purpose in the past, and it has turned out great. Basically, you arrange your fruit in between each layer, and spear a toothpick through the fruit and cake layers in a few key places. Fill in between pieces of fruit with your frosting. Enjoy the amazing combination of fruit, cake, and marshmallow!