I love an American sheet cake – it’s a great way to feed a lot of people and, in my book, the more people get to eat cake, the better. I’ve simplified what is an already simple approach, so that both cake, and icing/frosting are made in saucepans on the stovetop: in other words, no creaming and multi-stepped process, just melting, stirring and pouring. What’s more, this is an infinitely variable recipe (and see Witter for ways I alter this cake according to my whim) and a gratifyingly reliable one.
Traditional sheet cakes require buttermilk for sponge element, and this kind of icing/frosting needs regular milk. Rather than send you (or me) to the shops for an extra ingredient, I simply turn fresh milk into buttermilk by adding vinegar to the milk before I get on with the rest of the cake. It’s obviously not worth using an expensive vinegar, and if you wanted, you could equally use lemon juice. By the time you come to use it, the milk-now-buttermilk will look like a curdled mess, and that’s a good thing! The buttermilk is what helps keep the cake crumb so tender.
The batter is runny – and is meant to be, that’s what helps its fudgy texture later – and the cake will look woefully shallow once this mixture is poured into the tin. Do not be alarmed: it will rise, but not enormously; this is meant to be a shallow cake. It’s perfect for bake sales, birthdays, indeed any celebration, and now I happily offer it to you as a celebration of, and thanks, for reaching 1 million of you on my Facebook page.
Recipe posted by Nigella