What does cornflour do to the icing in the Ginger and Walnut Carrot Cake? I only know of cornflour as a thickening agent upon heat being applied to the mixture, but have never heard of it used cold like this. What does it do to the icing without cooking it?
Nigella's Ginger And Walnut Carrot Cake (from her new book AT MY TABLE) is topped with a buttery cream cheese frosting. The frosting includes a small amount of cornflour (cornstarch) as this helps to stabilise the frosting and prevent it from becoming too liquid.
The water content in cream cheeses can vary quite a bit (across both brands and countries) and some of the spreadable cream cheeses can contain higher levels of liquid than the traditional "bar" form of cream cheese. Sometimes the icing (confectioner's) sugar can dissolve in this liquid and give a runny frosting that is difficult to fix. Cornflour is very absorbent and when it is added to the frosting it will help to absorb any excess liquid, giving a frosting that is soft but not runny. The cornflour is added in fairly small quantities and usually doesn't leave any floury taste. Cornflour used to be added in small quantities to icing sugar to help to prevent it from caking into lumps (though now other additives are usually used), so has been indirectly used in buttercreams and frostings in the past.