I recently tried making the Blonde Mocha Layer Cake but the sponges both sank and then cracked, and the icing did not set properly. I followed the recipe to the letter with the one exception that I used half fat creme fraiche in the icing. What else could have gone wrong? Thanks.
Nigella's Blonde Mocha Cake (from Forever Summer) is a coffee-flavoured sponge cake with a rich white chocolate icing. As Nigella mentions in the introduction, it is quite a rich cake but there are times when you need something sweet. The cake base is a fairly standard all-in-one Victoria Sponge mixture that is flavoured with the very finely ground instant espresso powder. If the cake sank after cooking there could be several reasons but the most likely ones are that the rasising agents in the self-rasising flour had expired or the cake was not quite fully baked.
When using self-raising flour always check the expiry date on the packaging. Sometimes it is easy to let the flour sit in the cupboard for too long and the rasising agents in the flour will have expired, so the cake doesn't rise much. When baking the cake all ovens vary so make sure it is properly preheated and start checking the cake only a couple of minutes before the end of the baking time. If the cake isn't done then check again after another 5 minutes. Don't start checking the cake too early as opening the oven door can collapse the cake if it has not set sufficiently. The cake should feel firm to the touch, be shrinking away from the sides of the tins and a cake tester inserted into the centre should come out clean.
For the icing, the low fat creme fraiche could affect the icing as it will have a higher proportion of water than regular creme fraiche and this will make it more difficult for the icing to set. If the icing is too runny then refrigerate it and give it a stir every 5 minutes until it is thick enough to spread. If it is warm weather then it may also help to refrigerate the cake after icing, or keep it in a cool place.