Boy Wonder and his Rainbow Cake

When we were growing up my brother (Boy Wonder) and I had an unhealthy obsession with food colouring.  Anything that could be made a different, and hopefully a more disgusting colour was fair game. Our tongues were permanently shades of lime and violet much to Mother Hen's horror.  Boy Wonder's speciality was pancakes; one pancake batter a vivid flamingo pink another the deepest shade of aquamarine, then both swirled together so the finished item would make you trip a little. It was the only way to start the weekend.

Now I can't actually remember if I dreamt this cake or clapped eyes on it during a bizarre internet search (I'm hoping it was the first because god knows what I'd been searching for) but as soon as it was lodged in my head it was the only cake that could celebrate Boy Wonder's birthday properly.  Further investigation proved unfruitful, most 'taste the rainbow' cakes were not dissimilar to our old pancakes in appearances and I wanted to create something that was a bit more grown up but still magical.  So I got my pencil crayons out...

The dream was realised...

I have only started to master the art of the Victoria Sponge in the last year. This is down to a few simple rules that I have learnt and I would like to share that wisdom.

1. Make sure that the butter and eggs are at room temperature.  Leave them out for a few hours before.

2. Use an oven thermometer, ovens are crap and the wrong temperature will wreck your cake.

3. Never shortcut and miss out the greaseproof paper.

4. A spatula is your best friend.

5. Creaming the butter and sugar is the most important step, it must change colour completely and be a pale ivory. To get the best results use an electric whisk.

6. Adding a little flour with each egg stops it from curdling.

7. Eating the mixture will make you feel sick. Somehow I always seem to forget this.

The Sponge

To make the sponge for this cake I just doubled a basic Victoria Sponge recipe. I knew that each layer would have to contain at least one egg if they weren't going to pancake thin so doubling up from four to eight made sense.  The plan then was to make basic sponge, divide into 6 equal amounts, colour and then bake in pairs. I bought 2 shallow sandwich tins at a bargain £2 each, like these. This cake contains a lot of butter - almost 4 packets - please remember that it is a celebration cake and it happens to be huge so don't let it put you off.

8 eggs

450g (16oz) unsalted butter

450g (16oz) self raising flour

450g (16oz) caster sugar

pinch of salt

vanilla extract or 1/2 vanilla pod

food colouring - green, blue, yellow and red

Set your oven to 180c/350F/Gas Mark 4.  Fold a long length of greaseproof paper over six times and trace around one of the sandwich tins.  Cut around the trace making 6 identical circles of greaseproof paper.  Grease both the tins and place a piece of greaseproof paper in the bottom.

Cream the butter and sugar together until pale and fluffy, this may take some time but it's important.  Lightly whisk the eggs together in a separate bowl and, a bit at a time, beat into the sugar and butter - remember adding a spoonful of flour at the same time will stop the mixture from splitting.  Once all the eggs are incorporated sieve the flour and salt into the bowl and fold in with a large spatula or spoon.

Divide the mixture into 6 bowls (you can weigh this to make it properly accurate) and start to add the colour.  It must be as saturated as possible so don't be afraid to add more than you think.  Blue and red make the purple (more blue than red) and red and yellow are mixed for the orange.

Bake two of the sponges at a time for 10-15 minutes (mine took exactly 13 mins, test with the first two sponges and use this time for the rest).  When the other sponges are cooking place the others in the fridge covered tightly in clingfilm.  Once a skewer comes out clean and the top feels springy take them out of the oven and let them rest in the tins for 5 minutes before turning upside down onto a cooling rack.  The underside of the sponge is neater and smoother than the top which can rise unevenly therefore keep them this way.  Continue to do this until all the sponges are cooked.  The sponges can keep for a few days if properly airtight, alternatively they can be frozen too so make them in advance if time is tight. 

Decoration

To contrast with the technicolour interior I wanted the icing to be a brilliant white.  Buttercream is a rich icing so to cut through the sugar I added lemon zest and juice to give wee tang.  I watched a couple of icing technique videos on YouTube (rock and roll eh?!) and they were really helpful.

420g (15oz) butter

840g (30oz) icing sugar

1 lemon

In a large bowl beat the butter until soft, add half the icing sugar and beat until smooth.  Add the remaining icing sugar plus the zest and juice of the lemon and continue to beat until the mixture is full of air and significantly paler.  If the mixture is too stiff a drop of milk can be added.

Start with the purple sponge and spread a large tablespoon of the buttercream on the top, smooth it evenly and place the blue sponge on top of it.  Continue with this process with green next, then yellow, then orange and finishing with red. By this point there should be at least 2/3 of the buttercream left to cover the top and sides.  Start by placing almost half of the buttercream on to top, using a palette knife smooth over the top and down the sides creating a thin layer allover the cake.  Place the cake in the fridge for half an hour.  This technique is called crumbing (get me!) and seals in all the crumbs so they don't mix in with your icing and ruin the clean effect. 

Once the first layer has set, place the remaining icing on top of the cake and work down using a palette knife or spatula.  I used a hilarious gadget that my dear father was conned in to buying at Nick Nairn's cook school.  It is meant to be used for scrapping ingredients off the chopping board into the pan but why you couldn't just use your knife I will never know.  Anyway it was perfect for getting sharp edges along the top and a smooth finish around the sides (so good money well spent Pa!).

So there you have it, the rainbow cake.  Decorate with skittles for the full 'taste the rainbow' experience.  Also a handy cake to bring if you are coming out to your family.