The Chocolate Sheet Cake was to make, but mine was disappointing - flat, not very great tasting and icing too much! Did I do something wrong??
Nigella's Chocolate Sheet Cake is an easy stir-together sponge cake that is topped with a rich, slightly fudgy frosting. The cake itself is a single layer of sponge. If the cake is thin it could be that the pan used was too large, it should be approximately 33 x 28cm (13 x 9 inches), but if in doubt use a tin that is slightly smaller and a 30 x 20cm (12 x 8 inches) roasting tin or foil pan would work too. The raising agent is a combination of bicarbonate of soda (baking soda) and the vinegar used to sour the milk. If you did not sour the milk, or used less vinegar, then this could be the reason for the cake not rising properly. Also check that the bicarbonate of soda is within its "use by" date. Finally make sure that the oven is fully preheated before you start mixing the cake batter, as the bicarbonate of soda acts quickly and if the cake batter is left to stand then the bicarbonate of soda could fizzle out, causing the cake to rise less.
The icing should be poured over the cake while the cake is still warm. It slightly soaks into the cake, giving the cake and icing a slightly fudgy quality. The icing is quite sweet, but it is not a very thick layer so should not overpower the cake itself.