You will need to make this sponge recipe twice (so you will need to double the sponge ingredients below) to make six layers.
For the sponge
225g butter, softened
225g castor sugar
1 tsp (5ml) vanilla extract
4 jumbo eggs, at room temperature
225g self-raising flour, sifted
Food colouring – red, orange, yellow, green, blue and purple.
For the icing
100g butter, softened
1 tsp vanilla extract
½ cup (125ml) icing sugar, sifted (plus a little more just in case)
4 x 250g cream cheese
1. Preheat the oven to 180°C.
2. Lightly grease 3 x 20cm Push Pan cake tins and set aside. Cream the softened butter and sugar together using an electric beater or stand mixer until pale and cream in colour.
3. Add vanilla extract and eggs, one at a time, making sure you beat in each one before you add the next. Fold in the sifted flour and then divide the mixture into three mixing bowls making sure that the weight of all three mixtures is equal.
4. Pick three of the colours (remember you’re going to be making the recipe twice to get all six colours) and add a little into each batter bowl, adding more until you are happy with the colour. Be careful not to add too much colour in the beginning, as you can always add more food colouring to achieve a brighter coloured cake.
5. Pour each batter into the three prepared baking tins and place into the oven for about 15–20 minutes or until the cake is cooked and a skewer inserted into the centre of the cake comes out clean.
6. Remove cakes from the oven and allow to cool for a couple of minutes in the cake tin before gently pushing out and carefully placing on a cooling rack to cool completely. If the cakes rose with quite a peak in the centre you may want to trim this level with a bread knife. Don’t be disheartened by the dulled outside colour of the cake. The baked food colouring will look odd but the inside of your cake with be delightfully bright still, rest assured. Repeat this recipe using the remaining three food colour gels to achieve your six layer rainbow cake.
7. To make the icing, place the softened butter and vanilla extract into a large mixing bowl and, using an electric beater, cream until smooth.
8. Add in the sifted icing sugar and beat until well incorporated. Add cream cheese and whisk until smooth.
9. Taste the cream cheese icing and add more icing sugar if you would prefer a sweeter icing.
How to assemble a rainbow cake:
1. Smear a little icing onto a cake stand and place the purple coloured sponge onto the blob of icing. This prevents the cake from sliding around the platter. You may want to place your cake layers top side down, so that the flat ‘bottom’ faces upwards, this also ensures that your layers are even and less tapered.
2. Then spread a generous amount of icing onto the purple sponge, making sure you spread the icing right to the edge. Place the blue sponge on top of the iced purple sponge and repeat this icing process following with green, yellow, orange and finally red. Again, don’t fret if your cakes aren’t as bright as you expect them to be – the true colour won’t show on the outside.
3. Spread a thin layer of icing all over the cake to secure any loose crumbs on the surface of the cake.
4. Refrigerate the cake for ten minutes to allow the crumb coat to set. With the crumbs now secured, very generously smear the remaining icing all over the sides and top of the cake. Sprinkle with hundreds and thousands if you want a truly colourful cake or leave plain with the brightly coloured surprise on the inside.