You'll need 3 x these ingredients for six sponges
- 125g butter, softened, plus a little extra for greasing
Butter is made when lactic-acid producing bacteria are added to cream and churned to make an…
- 225g plain flour
- 150g golden caster sugar
- 3 medium egg (very important to use the correct size)
- 1 tsp baking powder
Baking powder is a raising agent that is commonly used in cake-making. It is made from an alkali…
- pinch of salt
- 1 tsp vanilla extract
- edible food colouring - red, orange, yellow, green, blue and purple, plus optional pink (see below)
For the icing
- 1 tsp vanilla extract
- 3 x 250g tubs cream cheese or mascarpone
- 350g icing sugar
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Heat oven to 180C/160C fan/gas 4. Grease 2 x 20cm round sandwich tins and line the bases with baking parchment. Tip all the sponge ingredients, apart from the food colouring, into a mixing bowl, then beat with an electric whisk until smooth.
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 12 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. Unless you’re making the optional pink layer, repeat one more time to get 6 sponges, all of different colours. Leave them all to cool.
To make the icing, very briefly beat the vanilla and cream cheese or mascarpone with an electric whisk until smooth. Sift in the icing sugar and gently fold in with a spatula. Be careful – the more you work it, the runnier it will get, increasing the chance of splitting.
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. For more tips and expert advice on how to create the perfect rainbow cake, check out our tips, below.
How to create the perfect colours
To make sure you’ve got a good balance of colours, test your colourings in a little water first – I tried over 20 shades before I found my favourite combination! Find out more about colourings
Tips for a professional finish
When you make each batch, keep a tiny blob of batter back – then, as you dye each future batter, you can make sure the colour strengths match. A palette knife, which has a long, rounded and flexible blade, makes icing big cakes much easier, as the blade is long enough to scrape the whole side at once. You can buy them in cookshops. A turntable really helps if you’re trying to ice a big cake. If you don’t have one, use a cake stand instead.
Which colours did we use
We used SK Professional Paste Food Colour and Quality Food Colour paste ranges from squires-shop.com. Buy pots in Red, Orange, Sunflower, Fern, Hyacinth, Purple and Pink. From the supermarket, try Dr Oetker gel food colours in Bright Red, Neon Orange, Sunshine Yellow, Lime Green, Sky Blue, Ultra Violet and Hot Pink. Read our top tips on colouring.
Trimming your sponges
We've kept the sponges as light as possible so they may be slightly rounded when they come out of the oven. You may want to trim them just a shade, to flatten so they all stack neatly together. We've answered your FAQs on sponges here.
Make an extra layer
My recipe makes six sponge layers, but you can make one extra layer by halving the cake quantities and baking a single sponge dyed pink – use this as your seventh layer. It’s not strictly necessary, the cake will still look fabulous with six – but why not! Click here for more tips on sponges.