Monday, 13 May 2013

Rainbow Birthday Cake

May appears to be the month of birthdays at Lincoln College, Oxford! May day is a big deal here, so on my birthday (May 1st) we all arose (fairly hungover) at 6am to watch the choir sing on Magdalen Tower, before heading to a champagne breakfast, followed by lunch a lot later on!

 I was absolutely spoiled on my birthday, in a way that completely overwhelmed me. Last week it was my good friend Rose's birthday, followed my Boo's birthday on the 13th May, and I was determined to spoil these two wonderful people and make them feel as happy as I did.

And it just so happened.. that in the middle of all these birthdays.. I went home! How could I NOT have made a birthday cake?!

I was inspired to make this particular cake, inspired once again by The Boy Who Bakes, due to a particular Mean Girls quote..

"I wish I could bake a cake filled with rainbows and smiles and everyone would eat and be happy..."

So that's precisely what I did.

225g unsalted butter
325g plain flour
50g cornflour
4 and a half tsp baking powder
1/2 tsp salt
400g caster sugar
2 tsp vanilla extract
4 medium eggs
300ml whole milk
gel food colouring in red, yellow, orange, purple, blue and green
150g white chocolate
300g caster sugar
6 medium egg whites
540g unsalted butter

Preheat the oven to 180 degrees Celsius (160 fan), then grease and line three 20cm round cake tins with baking parchment, greasing the parchment too. In a medium bowl, whisk the flour, cornflour, baking powder and salt together to combine, and set aside.

Put the butter in a large bowl and beat until smooth and light. Add the sugar until light and fluffy, about 5 minutes, then add the vanilla and mix to combine. Add the egg yolks, one at a time, beating until fully combined. Sift the flour in in three additions, alternating with the milk.

Put the egg whites into a clean bowl and whisk until they hold soft peaks. Add the whites to the cake batter and gently fold together until just combined and there are no streaks of white.

Divide the batter between six bowls. Add a small amount of colouring to each bowl, enough to make it a vibrant colour. Add the first three colours to the three tins and bake for 15 minutes or until they spring back when lightly touched. Allow to cool for 10 mins before turning out onto a wire rack to cool. Repeat with the remaining three colours.

To make the frosting, melt the chocolate in heatproof bowl set over a pan of simmering water making sure the base of the bowl doesn't touch the water. Remove from the heat once melted and leave to cool.

Put 190ml of water and sugar into a pan over a medium heat. Bring to the boil and have a sugar thermometer ready. Meanwhile, put the egg whites into a free-standing electric mixer. Start whisking the egg whites on high speed when the syrup in the pan reaches about 115 degrees Celsius on the sugar thermometer. Cook until sugar reaches 121 degrees. With the mixer still running, pour the syrup in a slow stream down the side of the bowl containing the whites. Continue whisking on high speed until the meringue is room temperature.

With the mixture still running on medium-high speed, add the butter in small pieces at a time, beating until fully combined. When adding the butter it can sometimes look curdled, but don't worry - just keep mixing and it will eventually smooth out to form a light buttercream frosting. Pour in the melted chocolate and mix until fully combined.

To assemble the cake, put the purple layer on a cake board and top with a thin layer of frosting. Repeat the process with the other cake layer in the order of the rainbow - purple, blue, green, yellow, orange, red and then spread the remaining frosting across the top and sides of the cake.

If you're making this for a birthday, you might also want to make these marshmallows as a cute homemade present!

I was darn pleased with the way this turned out, slicing into the middle and revealing the rainbow inside in the JCR with all my favorite people was pretty wonderful :) I hope they both enjoyed it!


  1. I have only made what I call tie-dye cupcakes, but after seeing your cake I will have to try this version.

  2. What an awesome suprise for those who cut in to it!! Fab cake Leah.
    I remember that bit from mean girls....that film was hilarious.

  3. I've been wanting to make one of these for a while. Yours looks absolutely fab! I also see that we have the same set of measuring spoons! Happy belated birthday :)

    1. Haha mine are from Lakeland! Can't bake without a trusty set of measuring spoons :) Thank you! x

  4. What a fun cake to make to slice into. I'd love to be able to apply the idea in a cake pop.

  5. What a fun cake! It looks so innocent on the outside but inside is where the party is. Love all the layers!

    1. Thanks! It was a bit fiddly but well worth the final effect x