Rainbow cake tips & tricks

Rainbow cake section

So todays post is about sharing some tips and tricks that I wished I had been smart enough to realise beforehand picked up when making Miss E’s rainbow cake. See, I’m making life easier for you!

Firstly, I will admit straight up that I used cake mix. I needed to make 6 layers of consistent cake and as I always say, Danni is the unattested Baking Queen of HYB! If I am doing a cake that requires a lot of time, fiddling and icing then I will generally use a mix to save additional stress. So I ended up using 4 packs of Green’s Buttercake Mix (tasted delicious btw)… I had two layers that I redid – the very first purple layer as I was trialling a silicon pan which didn’t work well for me (those of your who follow us on our facebook page would have seen that one), and the yellow layer as I wasn’t happy with the colour.

So for a cake the same size as Miss E’s – massive, we are still eating cake 4 days later – 3 packs of the Green’s mix is sufficient (not sure if the other brands are the same size), but I suggest to have an extra on hand to cover for mishaps!

I made up the batter then split it in half in separate bowls (measuring each so I got accurate halves). For the vibrant rainbow colours, I strongly suggest using the Wilton’s colour paste as opposed to the more liquid colour like Queens colour. After my Hoot the Owl cake wreck last year (I bravely posted it on our Facebook page), I learnt that you need a LOT of those little drops to get a darker and vibrant colour! I purchased just the red, blue and yellow colours as I figured I could mix the colour from the primary colours. It worked, but was a lot of fiddling and some of the colours did not come out how I would have liked. I’d suggest buying the actual end result colours if you can afford the extra outlay (I paid $4.95/each colour).

I started baking on Monday (party was on Saturday). This was just to make life easier for me as I knew I had a busy week ahead. I used a springform pan (our pans are all in storage, so it was either that or the silicon pan), I lined the base with baking paper and greased and floured the sides.  To prevent burning the small amount of batter in the pan, I baked in a slow oven, around 160 degrees (thanks to Danni’s DH for that tip). Because the oven wasn’t very hot, the cake didn’t rise much which worked well for my purpose, I was expecting to have to slice each layer in half but it wasn’t necessary, and the texture was still fine. Once each layer was baked and cooled I popped on a flat plate, wrapped securely in cling film and froze them. Bring each layer out of the freezer around 15 minutes before icing it. You still want them partially frozen as it will assist in icing without getting crumbs everywhere.

Oh and unlike me – put it on a nice board BEFORE icing! I still had it on a baking tray and it was too heavy and delicate to move off once iced…

Rainbow cake

Ultra bright-white buttercream icing

You’ll need:

  • 250gm room temperature butter
  • 250gm copha softened in the microwave until pliable
  • 1 tbsp + 1 tsp of clear vanilla extract
  • 7 cups of icing sugar (came out a TB short of 1kg for me – less than I had thought)
  • 6 tbsp milk
  • 1 drop of blue Queen’s food colouring – dropped into a teaspoon laid flat on your bench

Do this:

In your mixer bowl, thoroughly cream butter, copha and vanilla. Add one cup of icing sugar and one tablespoon of milk.

Beat thoroughly on a medium speed. Repeat the icing sugar and milk step.

Once you have added the third cup of sugar and TB of milk, grab a skewer or something that allows you to drop a tiny bit of food colouring into the mix. Drop in the colouring and mix thoroughly. This will neutralise the yellow colour from the butter.

You may need to add a little more, I found a couple of dabs was enough, though it probably could have gone one more, but was scared of the potential of turning it green…

Keep adding all of the milk and icing sugar cup by cup, beating in between*

Beat for an additional 5 minutes at medium speed.

This recipe made heaps of the buttercream. It was enough to cover the inside and out of my rainbow cake and I still had around a cup left over…

*If you are permanently suffering from baby brain as I am, I suggest a paper and pen nearby to keep track of your cups of icing sugar as you add them so there is no losing count!



  1. Mel has forgotten to mention that its BLUE food colouring you need to add to this icing. The blue neutralises the yellow in the butter, turning it white. However as she says…go easy! Less is more! You can keep putting it in but you can’t take it out!! ~ D

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