Rainbow Cake

This is MY take on the stunning rainbow cake.  I found the recipe on the Martha Stewart website but the cake was actually created by Whisk Kid.  The Marth Stewart recipe can be found here and she also has a video of them making it on the page if you want to watch it before you begin. I have made a few changes but nothing major.
There are a HEAP of ingredients, so this isn't a cheap cake to make, and certainly not a cake to eat if you are watching your weight.  In saying all that, when I cut into the cake I was so delighted and the kids 'oooohhhed'  and 'aaaahhhedd' which made the hours of preparation worth it!

Cake Ingredients
3 cups of standard flour
4 tspns of baking powder
1/2 tspn of salt
225 grams of butter at room temperature
2 1/3 cups of sugar
5 large egg whites at room temperature
2 tspns of vanilla extract
1 1/2 cups of milk at room temperature
Red, orange, yellow, green, blue and purple GEL food colouring

Preheat the oven to 180 degrees and brush an 8 inch round cake pan with butter.  Line the bottom with baking paper and then brush again with butter.  I used an 8 inch pan instead of the original recipe which uses a 9 inch pan as I wanted the sponge layers to be thicker, so up to you which size you want to use.
Whisk together flour, baking powder and salt in a bowl and set aside.  In a mixer bowl fitted with a paddle attachment, cream butter and sugar then slowly add egg whites until well combined.  Add vanilla and mix again until it is well combined.  Add a 1/3 of the flour mixture into the creamed mixture and beat slowly, add 1/3 of the milk and beat again, do this until all the flour and milk has been added.  Mix until well combined.
Divide batter evenly into six bowls and add enough of each food colouring colour to each bowl, then whisk.  The colour of the mixture will be the colour of the baked cake so add enough colouring to get the desired look you want.  It is SO important to use gel colouring otherwise the colours won't be vibrant enough.  I purchased my gel colouring from Millys.  Transfer each colour to a cake pan and bake for about 10-15 minutes (I cooked mine for 10 minutes but it will depend on your oven).  You can test by inserting a fork or tester into the middle, it is cooked if it comes out clean...no gooey mixture on it.  Make sure to spread mixture out evenly before cooking.
Remove cakes from oven and transfer onto a wire rack and cool for 10 minutes then turn over and let it completely cool.  Use a serrated knife to trim tops if you need to make them level.  I didn't need to do this with mine.
Starting with purple, lay the cake on baking paper, spread about 1 cup of buttercream filling over the entire layer, keeping it level, repeat process with blue, green, yellow and orange.  I even put a thin layer on top of the red cake as I had enough mixture and then I went around the sides and filled in any gaps and leaving a thin layer over the entire cake, all nice and smooth.
Lastly add the frosting layer over the top and sides.  I then used a hot dry knife (I dipped the knife in a bowl of boiling water then dryed) and slowly smoothed out the frosting.  Refridgerate until set.

I kept mine in the fridge until a few hours before the party.  I decorated with M&M's in the shape of a number 2 as this was for my little man's birthday.


Filling Ingredients
9 large egg whites
1 3/4 cups of sugar
450 grams of butter cut into small pieces at room temperature
2 tspns of vanilla extract

Cook egg whites and sugar in a small pot over a medium heat, whisking constantly until sugar is completely dissolved.  Test by rubbing some in between your fingers, if the mixture is smooth (no sugar grain) then it is ready.  Transfer to a mixing bowl fitted with a whisk attachment and mix on high for about 10 minutes or until the mixture has soft peaks like a pavolva mix.  Turn down the mixer to medium and add the butter one piece at a time, mixing well after each addition.  This takes time but don't rush it as you will have lumps of butter through the mixture at the end.
Remove whisk attachment and switch to paddle, increase speed to high and beat until the buttercream comes together (about 5 minutes) then add vanilla.

Frosting Ingredients
5 large egg whites
1 cup of sugar
225 grams of butter cut into small pieces at room temperature
1 tspn of vanilla extract


Cook egg whites and sugar in a small pot over a medium heat, whisking constantly until sugar is completely dissolved.  Test by rubbing some in between your fingers, if the mixture is smooth (no sugar grain) then it is ready.  Transfer to a mixing bowl fitted with a whisk attachment and mix on high for about 10 minutes or until the mixture has soft peaks like a pavolva mix.  Turn down the mixer to medium and add the butter one piece at a time, mixing well after each addition.  This takes time but don't rush it as you will have lumps of butter through the mixture at the end. 

This isn't necessarily a hard recipe, more time consuming but so worth it! Good luck and if you make it, post up a photo on my facebook page www.facebook.com/beckylipp - yay!