Chocolate Sheet Cake Cracking On Top

Our answer

Nigella's Chocolate Sheet Cake is a chocolate sponge that is baked in a rectangular roasting pan. The cake may crack very slightly on top but you don't normally see this as the icing is poured over while the cake is still warm.

However if the cracks are very deep then it is most likely that the oven is too hot. The outside of the cake bakes quickly, pushing the centre upwards and causing the surface to crack. The recipe gives oven temperatures for a conventional oven, so if you have a fan or convection oven then you will need to adjust the oven temperature following the guidelines in your oven's handbook (usually you reduce the temperature by 20c/50F but oven models do vary). For a conventional oven bake the cake on the centre rack and you may like to check the oven temperature with an oven thermometer. If you have a fan oven then it may also help to rotate the pan by 180 degreees after 15 minutes of baking, as in rectangular and square pans the corners of the cake tend to cook more quickly.