July 7, 2021
Rainbow Explosion Cake!
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A four layer funfetti sponge cake, with rainbow themed buttercream frosting, a chocolate drip and even more for the best rainbow explosion cake ever!
Rainbow explosion cake
So I was super lucky to reach three quarters of a million followers on Instagram the other day, so I thought I would make an insanely colourful and fun cake to celebrate the occasion! It may seem a bit OTT, but I am a baking blogger after all!
Obviously I only recently made my regular rainbow cake which featured all the colourful sponges, a white buttercream frosting and then lots of colourful sprinkles – so I thought I would switch that cake on its head and create this!
This rainbow explosion cake is based a lot on my funfetti cake sponge – because its a super easy cake to bake, but also so colourful! I did go a little too overboard on the sprinkles, and only had light brown sugar to hand, so my sponge did look a little dark!
The recipe uses caster sugar and I would recommend that over light brown soft sugar for sure – I also used these funfetti sprinkles in the cake because ones that work for funfetti in the UK are so hard to find, and I love these so much!
All the colours!
If you don’t already know, funfetti is like confetti in something, so a cake in this case, and its just fun! But because of the dots of colour in the sponge, I thought I would create a lot of washing up for myself and do a rainbow buttercream outside!
Yes… again… the rainbow only has six colours because it works out much easier, and they are so much more straightforward to do! Red, orange, yellow, green, blue and purple. You can obviously swap these colours up though if you use the recipe for anything!
I used the same colours for the buttercream in this rainbow explosion cake that I did in my other rainbow cake recipe because they work so well, and I am all about reducing the ingredients or added bits like colours that we have to buy!
The method of decorating the cake is fairly faffy if you want the perfect lines like me, but you can also just slap the buttercream on and hope for the best! The best start though is to use some of the base buttercream recipe to do a crumb coat to seal in any crumbs on the cake.
I used the same technique as I did in my mini egg drip cake (there is a YouTube video for this!) and piped rings of colours around the cake after its crumb coat, and then, used my classic large metal scraper to scrape around the edges of the cake to create the smooth and perfect finish!
For the rainbow explosion cakes drip I used a white chocolate drip, but added in some extra white food colouring to make it even brighter – as I just love the bright contrast! This is optional though – or you can add in some colour and make the cake even more colourful, its completely up to you!
With the leftover buttercream from the sides of the cake, I piped them onto a large piece of cling film into a long lines, and then rolled the clingfilm up tightly into a sausage and put this into a large piping bag with my favourite piping tip – I find this the easiest method of multicolour buttercream, but again its optional.
With swirls of the buttercream, some colourful sprinkles, and some random rainbow style lollipops and some gold candles I had my bright and wonderful rainbow explosion cake! This was randomly thrown together and sort of on the spot so hopefully this post made sense! I hope you love the recipe if you do try it though! x
Rainbow Explosion Cake!
- 500 g eggs (weigh eggs in shells)
- 500 g unsalted butter
- 500 g caster sugar
- 500 g self raising flour
- 75 g funfetti sprinkles
- 750 g unsalted butter (room temp, not stork)
- 1500 g icing sugar
- 1 tsp vanilla extract
- 1-2 tsp red, orange, yellow, green, blue, purple and white food colouring
- 200 g raspberry jam
- 180 g white chocolate
- 75 ml double cream
- 1/2 tsp white food colouring
- Rainbow sprinkles
For the Cake
- Preheat your oven to 170ºC/150ºC fan and line two 8"/20cm springform tins with parchment paper and leave to the side for now.
- Add the butter and caster sugar to a bowl and beat until light and fluffy.
- Add in the eggs, and self raising flour and beat again until smooth.
- Finally add in the funfetti sprinkles and fold through.
- Bake the cakes in the oven for 60-65 minutes (or until baked - test with a skewer).
- Once baked, leave the cakes to cool in the tin for 10 minutes before removing to a wire rack to cool fully.
- Once all of your cakes are cooled, you can make the buttercream.
- Beat the room temperature unsalted butter on its own for a few minutes to soften it and make it supple.
- Gradually add the icing sugar beating very well each time until its all mixed in.
- Keep beating and add the white food colouring and vanilla extract and beat for a few minutes.
- Get six small bowls, and add 300g of buttercream to each bowl.
- Split each cake into two sponges, so you have four layers.
- Using a 10" cake board, add your first layer.
- Add a couple tablespoons of the buttercream on to the sponge and smooth over. Add a couple of spoons of jam to the middle.
- Repeat with the second and third layers, and then add the last layer on top.
- Using the leftover white buttercream, smooth over the sides of the cakes and fill in any gaps and create a crumb coat.
- Refrigerate or freeze the cake on the board for an hour or so to chill and firm to make the next stage of decorating easier.
- Once chilled, using a spatula or small piping bags, pipe the colours of buttercream around the sides of the cake.
- Smooth over using a large metal scraper until the sides of the cake are smooth like in the photos! You may need to add in more buttercream as you go to get the finish you want but this is totally normal!
- Once this has been done, refrigerate again whilst you make the drip!
- Add the white chocolate and double cream to a bowl and heat in a microwave in short 10 second bursts stiring well each time.
- Once melted and combined, add the white food colouring and mix until smooth!
- Add the ganache to a piping bag and carefully cut off the end and drip down the sides of the cake. The more you push over the side of the cake with the piping bag, the further it will drip!
- Add the leftover buttercream to a piping bag by adding lines of each colour onto a large piece of clingfilm and rolling this into a sausage.
- Snip the end off of this, and add to a large piping bag with your favourite piping tip and pipe swirls of buttercream onto the top of the cake.
- Finally sprinkle on some sprinkles and leave the cake to set in the fridge fully.
- In the hot weather I store the cake in the fridge until it has been portioned.
- This cake lasts 4-5+ days once made!
- The colours that you use and what order are up to you, this recipe is just how I did it! You can swap up the order or whatever you prefer!
- You should avoid supermarket colours as they are not strong enough.
- In this recipe use:
- This red food colouring
- This orange food colouring
- This yellow food colouring
- This green food colouring
- This blue food colouring
- This purple food colouring
- This white food colouring
- This piping bag
- This piping tip
- This metal scraper
- This white chocolate
- These sprinkles in the sponge
- I used these tins!
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Hi Jane how thick does your cake turn out (prior to halving it)? Mine seems flattish and my srf is in date. Not sure if using a springform tin which then domed up have affected the rise
Hiya – these are relatively thin cakes and need to be as you are stacking 6 sponges in one go! x
I made this once before and it was insane!!
I’d like to make it again for a friends birthday but it needs to be dairy free… (eggs are fine)
Do you have any specific recommendations for dairy free butter/spread and will the icing hold as well on the outside?
Thanks so much! Literally every recipe of yours always turns out amazing!
Hiya! I usually use flora plant block – it should work well! Hope this helps! x
Hi Jane. Could you tell me where you got the rainbow swizzle sticks to decorate the cake from please
Hiya! I just got them from a regular sweet shop! Hope this helps x
Hi Jane. How important is the white food colouring for the ganache? The one you recommend is unavailable right now. Thank you x
Hiya! Without this, the ganache will be more of a yellow because of the white chocolate, so its really up to you! Hope this helps! x
Hi, how deep do the tins need to be – I have 8 inch x 3 inch – are these deep enough thank you !
Hi, I’ve bought a tub of buttercream to test my colours out for the rainbow cake. And I’ve got forest green but just seems a bit dark and just not quite the right shade. Any tips please?
Hiya! Try just adding less – you’d be surprised how much a little goes! Hope this helps! x
I found I had to make extra buttercream to crumb coat and fill cake.
Great recipe and instructions.
This looks amazing! I want to make it in some 9 inch tins, can you reccomend how much I should up the recipe by? Thinking an additional half again to the existing?
Usually 9″ is about 1/3 more of the recipe! x
It looks SO BEAUTIFUL!
If I wanted to halve the recipe and just make a double layer cake what should I adjust the cooking time to?
BTW, our family is on countdown until your new book comes through the letterbox!
As you’d be using one tin instead of two, the baking time remains the same. And thanks! x
Thanks for sharing, congrats for your followers on instagram, the cake looks amazing 🙂
What tin would you use if you didnt have spring form? i have 4 layer tins would these work?
Hi Jane, is that a Russian nozzle for the buttercream swirls? I’ve got one like it but the buttercream always sticks to the nozzle when I try and pull away and it drives me bonkers! My buttercream is fine through traditional nozzles and Russian flower nozzles, but not the one that creates these swirls. Any tips? Thank you, Grace
I’ve linked the piping tip I use on the post! x
I would like to make this recipe with 3 layers but 6 inch. Can I use the same amount of buttercream you have posted or will that be too much? (I am using 300 g of ingredients with 5 eggs.)
This looks amazing and tasty! And wow! Congratulations I’ve just spotted your book on Amazon! xx
Thank you and thank you!! x
Wow this looks incredible Jane! My daughter would love this. Do you think I could make the sponge chocolate instead and if so how would I do that please? Thank you for another amazing recipe xx
Thank you! I would use 425g flour, and 75g cocoa powder (and leave the sprinkles out!) xx