What birthday girl or boy wouldn’t be delighted with this brightly coloured rainbow cake, imagine their surprise when they cut into it.This colourful cake looks spectacular but is very simple to make.
- 125g butter softened, plus a little extra for greasing
- 225g plain flour
- 150g golden caster sugar
- 3 medium eggs (very important to use the correct size)
- 1/2 tsp baking powder
- 3 tbsp buttermilk
- pinch of salt
- 1 tsp vanilla extract
- edible food colouring – red, orange, yellow, green, blue and purple,
For the icing:
Heat oven to 160C/140C fan/gas 3. Grease 2 x 20cm round sandwich tins and line the bases with baking parchment. Place the butter, sugar and vanilla extract into a bowl and beat well to a creamy consistency. Slowly beat in the eggs, one by one, then fold in the flour, baking powder, buttermilk and mix well.
Working quickly, weigh the mixture into another bowl to work out the total weight, then weigh exactly half the mixture back into the mixing bowl. Pick 2 of your colours and stir a little into each mix. Keep going until you are happy with the colour – the colour of the batter now will be very similar to the finished cake, so be brave! Scrape the different batters into the tins, trying to spread and smooth as much as possible – but try not to waste a drop of the batter – a rubber spatula will help you. Bake on the same oven shelf for 15 mins until a skewer poked into the middle comes out clean.
Gently turn the cakes out onto a wire rack to cool. Wash the tins and bowls thoroughly, and start again from step 1 – this time using another 2 colours.
With an electric mixer on medium speed, whisk heavy cream until stiff peaks form (be careful not to overbeat, or cream will be grainy). In another bowl, whisk together mascarpone and confectioners’ sugar until smooth. Gently fold whipped cream into mascarpone mixture until completely incorporated.
Smear a little icing on your cake stand or plate – just a splodge to stick the first sponge. Start with the red, then spread with some icing right to the very edge. Repeat, sandwiching on top the orange, yellow, green, blue and finally purple sponges. Spread the remaining icing thickly all over the sides and top of the cake.