Chocolate hot-milk sponge fairy cakes

Preheat the oven to 180°C. Grease and line 4 x 15 cm springform cake tins with baking paper.
Cream the butter, sugar and oil until light and fluffy. Add the egg whites and beat well. Add the milk, buttermilk and vanilla paste. Sift in the dry ingredients and fold into the batter.
Divide the mixture between 4 bowls and pour the red juices into one bowl of batter. Gently fold until well combined. Repeat with the other juices so you have 4 bowls of different coloured batter, i.e. red, orange, green and blue. Add the grated turmeric to the orange batter (with the carrot juice).
Pour the cake batters into the greased cake tins. Bake for 20 minutes, or until a skewer comes out clean when inserted.
Spread the frosting onto each cake and sandwich together. Ice the top with the remainder.
Cook's note: Raspberry, carrot, turmeric, spinach, blueberry and beetroot create the subdued shades of this rainbow cake.