Why Doesn't My Chocolate Sheet Cake Rise Much?

Our answer

The Chocolate Sheet Cake is Nigella's version of the American chocolate sheet cake (sometimes called a Texas Sheet cake). It is slightly different to a British-style traybake, which is often made with a standard sponge batter and then iced once the cake has cooled.

The Chocolate Sheet Cake is supposed to have a fudgy texture. Not as squidgy as a brownie but not as airy as a chocolate sponge. The batter contains bicarbonate of soda (baking soda), which is activated by acidic ingredients, hence the "buttermilk" made from mixing milk with vinegar. The cake will rise, but will have a close, fine crumb and will not have the same structure as a Victoria sponge. What makes this type of sheet cake particularly different to a traybake is that the icing is made by warming the ingredients together in a saucepan and then adding the icing to the cake while it is still warm. The cake and icing meld together, giving the cake its unique texture. You may prefer to try Nigella's Chocolate Cake With Coffee Buttercream, which also has a simple stir-together method and a more traditional sponge texture.