Birthday Custard Sponge Buttercream

Our answer

Nigella's Birthday Custard Sponge (from FEAST) is made with custard powder. It is correct that custard powder is mainly cornflour (cornstarch), with some vanilla flavouring and yellow colouring added. It is safe to use the custard powder without cooking it. It is also worth noting that some icing (confectioners') sugars use cornflour as an anti-caking agent.

We have not found that the amount of custard powder used (4 teaspoons) gives a chalky flavour to the buttercream. However, if you are concerned then you could omit the custard powder from the mixture and add 1 teaspoon of vanilla extract and a drop of yellow food colouring instead. If you do this then it is less likely that you will need to add the boiling water, so check if the buttercream has a spreading consistency before adding any water. If the buttercream is too stiff then add the water a few drops at a time just until you get a soft spreading consistency.