For my sister’s birthday, I made her a secret rainbow cake and I used Tanya Burr’s recipe (here’s a link to her book: Tanya Bakes) but instead of leaving the icing a pretty, simple white, I did chocolate and decorated it to hell so my sister would be excited for the cake only to be more surprised when it was rainbow inside! It worked, of course, she nearly died a little bit and she definitely squealed when we cut it and she saw colours! So for the actual cake, I used Tanya Burr’s recipe, but for the icing, I used one from BBC Food mixed with a standard buttercream icing recipe.
For the cake, you will need:
675g butter, softened
675g caster sugar
3 teaspoons vanilla extract
675g self-raising flour
3 teaspoons baking powder
7 food colourings (I used red, orange, yellow, green, blue, pink and purple).
- Preheat your oven (gas mark 4) and line your baking tins (I only had 2 so I had to keep going back and forth lining them and baking the cakes so it might be a good idea to cut the 7 you’ll eventually need so that they’re ready to go!)
- In a very large bowl, cream together the butter (it’s worth mentioning your butter should be quite softened so if it hasn’t been out for a few days, microwave it the tiniest bit then stir and repeat this until the butter is fully soft else your batter will be lumpy!) and sugar. I found that once all the ingredients were in my bowl, my little scales could no longer cope with telling me the weight so beware you will need a huge bowl.
- Mix in the eggs and vanilla extract, but crack/whisk the eggs separately in a bowl or mug so that you avoid any shell.
- Add in the flour and baking powder and at this point it should form a smooth batter.
- Split it into 7 bowls as equally as possible (you could weigh it but my scales would not cope and died a little bit that day so I just did it by eye).
- Add in your dyes to each bowl and each dye is different so you may need a little but you may need a lot. I used nearly the whole tube of each dye because I wanted strong, bright colours.
- Bake your cakes in the oven for 18-20 minutes (honestly, mine took around 24 but I think each oven is different).
- Allow to cool fully and then you can ice!
For the icing:
150g good-quality dark chocolate
300g unsalted butter, softened
600g icing sugar
3tsp vanilla extract
milk, if needed to loosen.
For the second batch of icing:
350g icing sugar
4tbsp cocoa powder
- Melt the chocolate in a bowl over a pan of boiling water (don’t let the water touch the bowl!) and stir it to prevent sticking/burning.
- Allow to fully cool and then beat the butter in a separate bowl.
- Slowly add the icing sugar so that it doesn’t fly everywhere and then add the vanilla extract too.
- Fold in the melted chocolate and then you can add a bit of milk if it’s too stiff to work with.
- (For the second batch) Beat the butter until soft and then slowly add the icing sugar.
- Add the cocoa powder carefully and finally the milk to loosen it up.
I piped a small amount between each layer of cake and used an offset spatula to spread it across evenly. Then I stacked them all up (didn’t bother with a straw or piece of dowling to keep it steady and upright because I live life on the edge) and smeared icing all around the visible surfaces. Once I’d coated it pretty evenly, I piped on some fancy dots and some small flower-type shapes as well as sticking on some m&ms and maltesers. Finally, I used a tube of chocolate to pipe on the number 13 (it was her 13th birthday) and covered the whole cake in edible glitter! How great! It was huge and probably served around 20 or more people overtime so it would be great for a birthday party or any kind of party involving a fair amount of people.