For any of you game to try the magic rainbow cake here is a copy of the instructions I sent to a few friends. It really is quite easy so have fun!!
Ok guys, here is my invented techni-colour dream cake recipe. More experienced bakers might have a better way of doing this, but this is how I went about it. It really comes down to the food colouring. Ok, first the cake. I made three cakes, each a different colour. Try and get good quality gel icing colour as you will only need to use a tiny bit to get vibrant colour and it works for cake and icing. I did all of this in a kitchen aid with a paddle attachment but I think electric beaters would do the trick.
2 cups flour
2 tsp baking powder
4 eggs (beaten lightly)
1/4 tsp vanilla extract
Pre heat oven to 180 degrees Celsius.
Grease and flour a 20-25cm cake tin (if you have a spring base PERFECT)
Mix butter and sugar together.
Sift the flour and baking powder together and add to the butter mix, alternating a bit of flour for a bit of the beaten egg to get a really smooth batter.
Add the vanilla and food colour (a little bit at a time!)
The batter will be quite thick. Pour into tin , smooth out and give it a band to eliminate air bubbles. Bake in the oven for 30 mins.
This is what makes this cake a winner. You will need one batch of the following for each cake layer and then a double batch for the outside of the cake.
250g icing sugar sifted
80g unsalted butter at room temp
25ml whole milk
couple of drops of vanilla extract
Beat the icing sugar and the butter together in a freestanding electric mixer with a paddle attachment (or handheld electric mixer) on slow/medium speed until the mixture comes together.
Turn the mixer down to slow speed.
Combine the milk and vanilla in a separate bowl and add to the butter mixture a little at a time.
Once all the milk is incorporated turn the mixer up to high speed and continue beating until frosting is light and fluffy (at least 5 mins) add your colour at this point so it is totally incorporated.
Slice the tops off your cakes so you have three even, flat layers.
Choose which colour you want on the bottom and make one batch of the frosting in the same colour. Smooth the icing quite thickly over the cake, leaving a little to one side.
Place your next cake layer on top. fill in any gaps around the outside with the frosting and scrape off the excess. Make another batch of frosting the same colour as the middle layer and repeat the process with the final layer of cake. Once your third cake layer is on top make the double batch of icing to cover the entire top and sides of your masterpiece.
Decorate any way you see fit! We used multi-coloured choc rocks and edible glitter. H got this stuff and the food colour from a cake decorating shop in Melbourne which has an online store - I can highly recommend, http://cakedeco.com.au/
If my instructions are hard to follow feel free to call me (or invite me over and we can do it together - I'll even bring my colouring ;)
Good luck cake lovers - and once again thanks to L for the inspiration and inspired method of getting those sprinkles onto the side of the cake!