Rainbow Cake Recipe

A delicious and bright rainbow cake with vanilla buttercream frosting, a pink drip and sprinkles! This is a proper showstopper. Six bright sponge layers, all baked from scratch, stacked up in 8″/20cm cake tins making a seriously tall but showstopping cake.

You bake the cake in two easy batches of three, smother the lot in whipped vanilla buttercream, and finish with a bright and signature pink drip with rainbow sprinkles. It looks like a lot, but I promise you it’s worth it and easily achievable.

What you need for this rainbow cake

So before we get stuck in, here’s the lowdown on what you need and why it matters, because a few little things really do make or break this bake:

• Eggs, unsalted butter, caster sugar and self raising flour. This is a classic weigh-the-eggs sponge, so the four main amounts all match each other. That’s the secret to a lovely even bake every single time.
• Food colouring, and this is the big one. You really do need good quality gel or paste colours (I share the exact ones I use further down). The watery supermarket bottles just won’t give you those insanely bright layers, honestly.
• Unsalted butter for the buttercream. Room temperature, and definitely real butter, not a baking spread . Real butter beats up whiter and holds its shape so much better.
• White chocolate and double cream. These are for that gorgeous pink drip, plus a little pink gel colour to make it POP.
• Rainbow sprinkles, as many as your heart desires!
• Equipment wise you’ll want three 8″/20cm springform tins, a large metal scraper, a small angled spatula, a 10″ cake board and a couple of piping bags. Nothing fancy, I promise.

A rainbow cake disclaimer

So… I will say from the beginning that this recipe uses lots and lots of ingredients, and it is a humongous cake! Like, its 6 layers of cake, and all the buttercream in-between the layers, and all the decor on top! 

And I will also say from the beginning… YES I KNOW THE RAINBOW HAS SEVEN COLOURS. This cake, is only six. When baking this cake, I just find making 6 colours so much easier, and you can see the obvious differences. I am not bothered about the seventh! 

Red, orange, yellow, green, blue and purple… the main colours you need in your life. I did slightly compensate for the lack of seven colours by adding in a pink drip on the outside but we will get to that later. 

Making the sponge

A few quick notes before I waffle on too much… as you’re making six sponge layers in two batches of three, you will only need three 8″20cm tins. Bake at 160ºc/140ºc fan, a touch lower than a normal sponge, to prevent the colours from browning and becoming dull.

For this cake, I did make probably the biggest one tier cake ever. It’s about 8-9” in height, and uses so many ingredients. Because it is a six layer cake I decided to make it in two batches. So three layers at a time, so therefore you still only need three tins! 

I made the cake a 600g mix, so that it’s super easy to split into two batches. The best way is to weigh 5-6 medium eggs, and get as close to 300g as you can, for example 312g, and then match the butter, sugar and flour to that weight.

Baking with colour 

Then, you mix it all together like normal, and then split into three bowls. It doesn’t matter which colours you do first, but I did red, orange, and yellow together, and then green, blue and purple.

The oven temperature is a bit lower than normal, as I don’t want the sponges to brown too much. This also comes somewhat from the brands of colours that you use! Red food colouring, orange food colouring, yellow food colouring, green food colouring, blue food colouring and purple food colouring. for the sponge mixtures!

One thing I can’t say enough… use gel or paste colours, not the watery supermarket ones, as the gels give you that vibrant punch without loosening your batter. And try to keep your three portions as even as you can (a quick weigh of the bowls really helps!), so every layer bakes to the same lovely height.

Making the buttercream

Once my sponges are baked, I leave them to cool completely and freeze them wrapped in clingfilm over night so that they are easier to decorate the next day – but this bit is completely optional of course!! 

For the buttercream, you do use 750g unsalted butter and 1500g icing sugar, which technically is a little obscene but the amount of servings from this cake is huge so please don’t be a negative Nelly about the sugar content! 

I make my buttercream like normal by beating room temperature unsalted butter on its own for several minutes to make it really loose and supple, and then I gradually add in the icing sugar! I make sure to beat this for quite a long time. 

You’re after a really soft, spreadable, almost fluffy texture here. If it ever feels a bit stiff or claggy, just beat in a tiny splash of milk, a teaspoon at a time, until it’s lovely and smooth again. Better to add a little liquid than to fight with stiff buttercream when you’re trying to get smooth sides!

White food colouring 

You can do several methods to get whiter buttercream, by beating the butter on its own for a lot longer, or using a smidge of purple buttercream to counter act the yellow, but I love using this white food colouring! It looks amazing on my white chocolate drip cake and I haven’t looked back since.

I add a little at a time and keep beating it very well to make sure its really white and bright to contrast against the colours of the sponge! Making the buttercream whiter is completely optional of course though. 

Decoration

When I am starting to decorate the cake, I dollop a few tablespoons of buttercream onto each sponge and smooth over, making sure to get the order of the colours in the sponges correct of course…! 

Once you have layered each sponge you need to do a crumb coat by using as little buttercream as possible around the edges to seal in the spare crumbs from the sponges! I then chill the cake for a while to firm it up before adding another layer of buttercream on top. 

I use a large metal scraper to decorate the sides of the cake, and a small angled spatula to also help cover the sponges – and its much easier and you are going to get a smoother finish using these as well! 

Sprinkles and drip

Just as I have finished the buttercream I carefully press in some rainbow sprinkles to the bottom of the cake for a bit of colour and I just love the design – be warned, sprinkles will fall off at this point so beware! After this, I chill the cake again! 

For the pink drip, I use white chocolate ganache with this pink food colouring added in. Its a super bright colour so you don’t need add too much and it means you get the best coloured drip ever! 

Pro tips for the best rainbow cake

I then pipe on the leftover buttercream, add on some more rainbow sprinkles, and the best cake ever is finished! I am forever in love with those sponges and how bright and pretty they are. But before you dive in, here are the little things that really make all the difference:

• Use good quality colours. I know, I keep banging on about it, but supermarket colourings will NOT work as well, or maybe at all, so please don’t waste your ingredients. Good gels are 100% worth the investment and they last for AGES.
• Level your sponges. If any layers dome up in the oven, trim the tops flat with a serrated knife before stacking. It keeps the whole cake straight and beautifully tall.
• Don’t overmix the batter. Once the flour’s in, beat until just smooth and no further. An overbeaten sponge bakes tougher and is more likely to sink on you.
• Cool completely before frosting. Warm sponge melts buttercream every single time. Fully cool, or use my freeze-overnight trick, is always the way.
• Chill between coats. Crumb coat, chill, then final coat, then chill again. Cold buttercream scrapes to a much sharper, smoother finish.

Rainbow cake FAQ

Can I make this rainbow cake ahead?
Yes, and I actively recommend it! You can bake the sponges a day or two before, wrap them well and keep them somewhere cool, or freeze them (see below). Splitting the baking and the decorating over two days makes the whole thing so much more relaxed.

Here’s my favourite little trick: once the sponges are completely cool, wrap each one in clingfilm and freeze them overnight. Decorating a slightly frozen sponge is SO much neater, they don’t crumble, the buttercream grips beautifully, and you get a cleaner finish with way less stress. Total game changer.

How do I store leftovers?
This cake keeps for 4-5+ days once made. In warm weather I keep it in the fridge until it’s been portioned, then it’s happy in an airtight container. Just bring your slices back to room temperature before serving so the sponge is soft and the buttercream isn’t rock hard.

Can I freeze rainbow cake?
Absolutely. You can freeze the plain sponges wrapped in clingfilm for up to 3 months, or freeze finished slices (open freeze them first, then wrap) for up to 3 months too. Defrost in the fridge overnight and you’re good to go.