So I’ve thought about baking a rainbow cake for a very long time and I’ve always thought of it as waaaaaaay too much work. Recently though friends of mine have asked me to make one as a birthday present and as it turns out, it really isn’t that much extra work, provided you’ve got at least 2 sandwich tins, otherwise baking six or seven sponges – depending how many colours you’d like your rainbow to have – might take quite a while.
I’ve gone for six different colours, which is not to make any kind of statement, but because I had 3 tins and I wanted to make the sponges in two stages. I would like to point out though that, since we’re still in lockdown and the rainbow has adopted a new meaning in which we support all the front line workers, that keep us safe, but also, after last weeks announcement that the London Pride Parade this year has been cancelled, this cake is for all of those people affected and everyone else who is having a hard time. Because cake makes people happy, it looks and tastes fantastic and it’s got sprinkles on it and who doesn’t like sprinkles???????
If you have six tins that all have the same size and you can fit them all onto the same shelf in the oven you can prepare the full amount of batter, if you only have three and/or can only fit three on one oven shelf prepare half the batter first and bake them all on the same shelf to ensure that they bake evenly, then repeat the same with the other half. If you only have two tins obviously prepare and bake a third of the batter at a time.
- 6 medium Eggs
- 300g Caster Sugar
- 150ml Buttermilk
- 150ml Vegetable Oil
- 225g Plain Flour
- 75g Cornflour
- 30g Baking Powder
- Pinch of Salt
- 1 Tbsp Vanilla Extract
- Gel Food Colours (Wiltons, Americolor, PME)
- 700g Soft Unsalted Butter
- 1250g Icing Sugar
- 2 Tbsp Vanilla Extract
- 2-3 Tbsp Milk
Grease and line your sandwich/ springform tins. Preheat the oven to 170 degree C.
In a large mixing bowl whip eggs and sugar with a hand mixer or the whisk attachment on your stand mixer for about 4-5 minutes until they’re light and fluffy. Add the vanilla extract, oil and buttermilk and combine it slowly.
Combine cornflour (makes the cake layers a bit fluffier), flour, baking powder well, then sieve them into the rest of the batter. Gently fold the dry ingredients into the wet, it’s key to not knock out too much air now! When the ingredients have just about combined, divide the batter into six bowls and colour them in with your gel colours: yellow, orange (mix from yellow and red), red, purple (mix from blue and red), green (mix from blue and yellow) and blue. Again be careful when mixing the colours in, the more air you knock out of the batter now the denser the cake will be, but don’t worry, we’ve added more baking powder in this recipe to still give the layers a good lift!
Pour each batter into a sandwich tin and bake them in the middle shelf of the oven for about 15-20 minutes. Keep an eye on them and take them out as soon as it springs back when you lightly push a finger into the top or a skewer comes out clean. Also be aware that many ovens are hotter in some places than others, so one cake layer might be baked before the others are done.
Let the layers cool down completely.
To prepare the buttercream beat the soft butter in a large mixing bowl with your hand mixer or the paddle attachment on your stand mixer for about 5-7 minutes, until the butter is nearly white in colour and very fluffy in texture. Sieve the icing sugar in in 3-4 stages, beating it until the icing sugar has been fully incorporated before adding more, and add the vanilla extract.
The buttercream wants to have a soft texture so you can easily spread it around the cake so you want to add a few tablespoons of milk if needed, until you have a good spreadable consistency!
Put the purple cake layer onto the middle of a cake board or cake lifter. If you don’t plan on moving the cake onto a stand or plate after you’ve finished decorating it you’ll want to secure it with a blob of buttercream. It’ll be easiest to decorate your cake on a cake turntable.
Take a large spoonful of buttercream, blob it onto the first cake layer and spread it out using an offset pallet knife. Make sure that you finish with an even layer of buttercream that spreads out all the way to the edges of your cake layer. Spinning the turntable while holding your pallet knife parallel to the cake will make spreading your buttercream out easier.
Repeat this with the other layers. Next blue, then green, then yellow, then orange and finally red. Make sure that each layer is centered and right on top of the last one.
Place the fridge in the cake for 30 minutes.
If the edges of the cake aren’t completely even take a bread knife and even the sides out, making sure that they are completely straight. Now add a large blob of buttercream to the cake and cover it in a thin layer of buttercream. This is called the crumb coat and locks all loose crumbs in so that they can’t get into the final layer of buttercream. This will also give you the chance that there aren’t any spaces left between the layers are filled with buttercream. Use a cake scraper to scrape off any excess buttercream (don’t put it back into the bowl, in case there are crumbs in there!) Place the cake in the fridge for at least another 30 minutes.
Now cover the cake in a thick layer of buttercream using your pallet knife. Hold an offset pallet knife parallel to the top of the cake while spinning the turntable to push excess buttercream off and create a smooth, even top. Then use a cake scraper to smooth the sides out. If there are any holes in the buttercream, fill them up and repeat the process until the sides are smooth. Finally take a clean pallet knife to pull any excess buttercream on the top into the middle of the cake.
Add a star tip nozzle (I used a Wilton 1M) to a piping bag and cut the tip off. Fill it with the remaining buttercream and give it a good shake to get rid of air bubbles trapped in the buttercream. Pipe a boarder around the top edge of the cake. Apply even pressure while holding the piping bag at a slight angle, moving it in a circular motion while slowly turning your turntable (watch the video, I find it very hard to explain how I’ve done it).
Finally sprinkle sprinkles over the top of the buttercream boarder and push them into the sides of the cake creating an ombre effect where the amount of sprinkles thins out towards the top.
All done. Really easy, as promised, and super yum!