I have baked the Chocolate Guinness Cake with great success previously, but the last two times it has had large cracks in the top. What would cause this? They are like the Grand Canyon!
Cakes can crack on top during baking and usually the cause is that the oven temperature is too high. As the cake bakes the outside edges and top form a crust quickly, then as the centre of the cake bakes it rises and causes the crust on top to crack. This is more common with denser cakes, such as Nigella's Chocolate Guinness Cake (from FEAST.
If you have a fan oven then make sure that the temperature has been adjusted according to the manufacturer's handbook. For a regular oven you can try checking the oven temperature with an oven thermometer to make sure that the thermostat is working properly. Also avoid opening the oven door too often, as this can cause fluctuations in temperature and can make it more difficult to bake the cake properly. Fortunately any cracks in the top of the cake can easily be covered up with the cream cheese icing.