I have learned a little bit more about how cakes work from revising and expanding my cookbook, Don't Sweat the Aubergine, for a new edition to be published by Black Swan in the spring. It made me think again about Elizabeth David's simple and delicious chocolate cake, which is often somewhat compacted after a day or so. If the egg foam cannot sustain an airy texture for very long, would the cake not benefit if one creamed the butter and sugar as well? Indeed it would. I have added a note to the original recipe.