I made this cake a few weeks ago with a friend for her office bake off. I’ve made rainbow cakes before (usually in time for the LGBT Pride parade!), but have never made it with so many layers! It’s a bit time consuming but it’s totally worth it for the effect. The picture above is of one I saw at the Real Food Festival (on Southbank, London on weekends) and the one below is a slice of the one I made. I adapted the recipe from on one from the amazing Sweetapolita (do check out her incredible blog!) – hers was covered in fondant icing and then doodled on with icing pens! Very cool. For this one, I used buttercream but I think next time I would make it with meringue frosting. To get the colours so bright you really have to use gel or paste professional food colourings. The shop bought little bottles of liquid will not give you the same effect. I use Sugarflair, which you can buy online here.
You will need:
- 250g butter, soft
- 475g sugar
- 5 egg whites, room temperature
- 2 tbsp vanilla extract (try and get the real stuff, not the cheap flavouring)
- 380g plain flour
- 4 tsp baking powder
- Large pinch of salt
- 1 1/2 cups of milk, warmed for 30 sec in microwave to bring to room temp
- Red, orange, yellow, green, blue and purple gel or paste food colouring
- And 8″ loose based round cake tins
- Butter, oil or cake release for greasing
- 4 large skewers
- A kilo of icing sugar, sifted (you may need spare)
- 200g butter (you may need spare)
- 50mls milk (you may need spare)
First of all, preheat your oven to 180°c degrees and grease your tins. I only have two so I just cooked them in 3 batches.
- Pop your sifted flour, baking powder and salt together in a bowl and mix well.
- In a stand mixer (or with a handheld electric whisk), beat together the sugar and butter until smooth and fluffy.
- Add the egg whites one at a time and beat until smooth. Add your vanilla and beat the mix on high until it is nice and fluffy.
- Then, alternating between the milk and the flour mix, add everything to the fluffy eggy mix. Mix on low speed until well combined and smooth.
- Split the mix between 6 bowls (you can do this by weight or just by using your judgement), and then add some fool colouring to each bowl so you have one of each colour. You might need to add a fair bit to get the vibrant colour. I just mixed it in with a dessert spoon bu you can whisk it if you prefer.
- If you’ve got two (greased) pans, pour the purple mix into one and the blue into the other and bake for 15-25 mins. Keep a close eye on it as the layers will be much thinner than your average cake layers.
- When the cake springs back, remove from the oven and leave to cool for at least 10 mins before removing to a cooling rack. Again, be very careful as the layers are thin and prone to breaking. Cool on a rack while you re-grease the pans and do the next two layers. Do the same for each set of layers until you have 6 sponges out of the oven.
- While they are cooling, pop your butter and half the sifted icing sugar into a standmixer with the milk. Beat slowly until smooth, then add the rest of the sugar.
- Once the sugar has stopped throwing up powder, beat on high until it is smooth and fluffy.
- When the cakes are cold, pop the purple sponge on a cake plate and spread a layer of the icing over the top. Carefully place the blue layer on top and do the same.
- Ice each layer until you have all six sat on top of each other. Because of the weight of the cake and the style of icing, you may find the cake layers starting to slide around. If that happens, stick the four skewers in a square shape through each of the layers to hold it all in one place. While it is being held, spread a layer of icing around the outside and top of the cake. Don’t worry if you get crumbs in the icing – you’re going to do another layer.
- Leave for a couple of hours until the icing sets and then add another layer around the outside and the top. If you used a lot in the first round, you may need to make some more. Just half or quarter the recipe for the buttercream to make a bit more.
- Use a pallet knife dipped in boiling water to spread it smoothly (and remove the skewers and smooth over the holes).
- Voila! You are done! My friend Lucy added skittles sweets to the outside of the cake, which looks cute, or you could add a layer of fondant icing on top, a la Sweetapolita. Or, use the meringue icing recipe I linked to above. I think I’m going to try that one next time because it’s incredibly white, which means the colours are super bright in contrast.