When I say that this cake only needs four ingredients I mean the frosting too. And what’s more, it’s completely gluten free and dairy free. It’s easy to make and light as a feather. In short, it’s a pretty magical cake that makes you realise you can do so much with just eggs, sugar and corn starch (the fourth ingredient is a 1/2 teaspoon of cream of tartar, which you could even leave out if you were very, very confident about your egg whites and then this would be a three ingredient birthday cake!).