I want to know why is there baking soda in the Love Buns but not in the Victoria Sponge Cake? I am trying to make the Victoria Sponge cake using plain flour so I have added 3 tsp of baking powder. But when I convert the love buns into a cake with double the recipe it sums up to 4 tsp of baking powder and 1 tsp of soda. So which one is correct and which one to follow to make the cake?
Nigella's Love Buns (from FEAST) are small sponge cakes topped with a soft swirl of marshmallowy icing - perfect to share on Valentine's Day or when a sweet treat is needed. The batter includes both baking powder and bicarbonate of soda (baking soda) to make sure that the cakes rise with a peak in the centre. The bicarbonate of soda acts quickly and helps to make the cakes rise more dramatically. This peak helps to act as a support for the swirl of icing on top - if you piped the meringue icing onto a flat-topped cake then the icing would sink back rather than staying in a peak.
For Nigella's Victoria Sponge (from HOW TO EAT and HOW TO BE A DOMESTIC GODDESS) a flatter top on the cake is more desirable so the recipe uses self-raising flour, which only contains baking powder. If you are using plain (all-purpose) flour then you should use 2 teaspoons of baking powder for each 150g of flour. For Nigella's particular recipe then you only actually need 2½ teaspoons of baking powder, though 3 teaspoons would be fine as the recipe also contains some cornflour (cornstarch). If you use a food processor then an extra teaspoon of baking powder is added as the butter and sugar are not creamed together initially, which helps to incorporate some air, so the cake batter needs a little extra lift. However you should not need to add any bicarbonate of soda.