I’ve made the Birthday Custard Sponge several times and loved it. But yesterday when I made it, it rose much more than usual and was dry and rubbery. Where did I go wrong?
Nigella's Birthday Custard Sponge (from FEAST) is a victoria sponge style cake made golden with the addition of custard powder. The buttercream has some custard powder added too. The cake itself is made in a food processor using an "all-in-one" method. Often if cakes have a rubbery texture then they have been overmixed. This can be easy to do in a food processor and if yours works at particularly high speed then we would suggest pulsing the ingredients until they are just combined rather than just letting the processor run for a few minutes.
The other possible reason is that too much leavening (baking powder and bicarbonate of soda/baking soda) was used. When this happens the cake will rise up a lot and then sink back, leading a denser, more rubbery texture. Quite often the surface of the cake will also look wrinkled if this happens. Measure the leavening with a 5ml measuring teaspoon and a 2.5ml half teaspoon and use flat spoonfuls. Also make sure that you don't accidentally get the baking powder and bicarbonate of soda the wrong way around.