what's cooking good looking?: Rainbow Cake!

Because it is my birthday tomorrow, and I'm turning 15 (yes, that's right. 15. uberly-dooberly excited!!) I made myself a birthday cake.
That sounds really lame. Nobody should bake their own birthday cake. However, no one was willing to make a cake for me, so my friend Marlin and I made a rainbow cake, consisting of four layers of sponge: red, yellow, green and blue. We then covered it in vanilla buttercream icing.

Yum.

(I apologise in advance for any hideous pictures of me. Fair to say I wasn't looking my best)

Ingredients

FOR THE SPONGE
400g unsalted butter, plus extra for greasing
400g caster sugar
2tsp vanilla extract
8 medium eggs
400g self-raising flour
food colouring

FOR THE ICING
420g butter
840g icing sugar
4-5tbsp milk
1tsp vanilla extract

I couldn't find a definite recipe for rainbow cake so I kind of had to make one up.

CAKE RECIPE
Heat oven to 190C/170C fan/gas 5. Grease and butter the sandwich tins. Place the butter, sugar and vanilla extract into a bowl and beat well to a creamy consistency. Slowly beat in the eggs, one by one, then fold in the flour and mix well.
Divide the cake mixture equally into bowls and add enough food colouring to create the colour desired. Then, transfer the coloured mixture into the cake tins, place in the oven and bake for about 20 minutes until risen. Check that they are cooked, and then turn out onto a wire rack and cool completely

FOR THE ICING
Beat the butter in a large bowl until soft. Add half of the icing sugar and beat until smooth.
Add the remaining icing sugar and two tablespoons on the milk and beat until the mixture is creamy and smooth. Beat in some milk, if necessary, to loosen the mixture.

You will need 4 sandwich tins to create four layers, but as I only had two, I did the ingredients for the sponge in two batches.

Marlin, my co-baker for the day, and I have always wanted to make a rainbow cake. We'd seen so many pictures on Tumblr, and it was time to make our own.

We wanted bright, bright colours, and only achieved this through lots (and lots) of food dye.

When the mixture was as colourful as we wanted it to be, we transferred it to the tin, and made lots of mess.

After 20 minutes in the oven, the first batch (blue and green) were done, but went a little brown, so we decided to try the next batch at 15 minutes.

When we took the second batch out of the oven, they seemed fine and cooked. But when we left them to cool for 5 minutes, everything went wrong...

The entire structure collapsed, as part of the cake wasn't cooked (though when we tested several parts of the cake with a skewer it seemed fine) and made a total mess. It looked unrepairable, until we somehow managed to stick it back in its tin (with lots of effort and moments of fear) and put it back in the oven.
It didn't look its best, but that didn't matter, as the whole cake would be covered in buttercream icing.

When all the cakes were finally baked, and they were layered in order of the rainbow, we made the icing.

WE WERE DONE!! The cake doesn't look its best on the outside, but we covered it in sprinkles, stuck some candles in and everyone sang Happy Birthday to me while I stood there awkwardly, not really knowing what to do with myself.