What Went Wrong?

Our answer

Usually if a cake is drastically shrinking away from the sides of its tin then it has been overbaked, though has not got to the stage of actually burning. We suspect that this is probably the case with your cake. Fan ovens cook more quickly than regular ovens and do normally need to be turned down. Usually the rule of thumb is to reduce the temperature by 20c (50F) for a fan oven though it is best to consult your oven manufacturer's handbook for specific advice. It is also worth checking the cake slightly early as all ovens cook slightly differently. The recipe suggests checking after 40 minutes, even though the cooking time is 50 minutes.

There is also a chance that the cake batter was overmixed - this would give a tough texture to the cake. Once the flour has been added to the food processor you should only need to whiz for a few seconds to combine the flour. If you are not sure then switch off the processor, add the flour and just use a few pulses to incorporate the flour into the batter.