Rose celebrated her birthday recently, and part of my gift was an insanely large, 6 layer rainbow cake! It took me a couple of days and was rather difficult to transport, but it turned out beautifully!
I’d never made one before so I did a bit of research and came to a couple of important conclusions. The first is that these cakes need a LOT of frosting to glue them together, so it had better taste really good! The second is that just colouring a vanilla sponge was practically false advertising. Take it from the girl who taste tested a lot of those scented textas and was always extremely disappointed… flavour is important!
I decided on a cocktail of fruit flavours that would harmonise together well, and chose for Red – Strawberry, Orange – Peach, Yellow – Passionfruit, Green – Pear, Blue – Blueberry, and Purple – Grape. I chose Lorann Oils as they offered the range of flavours I was looking for. Each layer was basically a whole cake, I used about 1.2 to 3/4 of a 1 dram bottle but could have gone to a whole bottle each I reckon. The tastes are not like the real fruit, but ‘lolly’ fruit versions, which suits this cake pretty perfectly. For really strong colours I prefer the food colour gels. I’ve always used Wilton, which are great, but for a couple of these colours I decided to try Americolor Soft Gel Pastes which I preferred as they are much less messy to use. The purple and green layers in my cake are Americolor, the rest are Wilton.
Start by buying ingredients. A LOT of ingredients! I ended up going back for more eggs and icing sugar!
Start with a test batch – check out colour and flavour intensity after baking.
Mmmmmmmm now make all the separate layers. I used a simple vanilla sponge and substituted half the vanilla with other flavours. Separate each mix into 2 bowls and colour and flavour.
Pour into lined cakes tins. I have three that are identical for baking layered cakes. 
Next, make up a huge quantity of buttercream. I chose an American Cream Cheese Buttercream for better flavour, it is a crusting type, which means it dries comparatively hard. Good for gluing lots of cake together. 
Then, I trimmed all the cakes flat, and started to stack them. The outer layer of the cake will always be golden brown, I trim off anything crusty as it can make a big cake like this more difficult to cut.
Once all the layers are stacked, Add a thin crumb coat, and leave in a cool room to set overnight. This is how I transported the cake all the way up to Monarto Zoo where the party was! The reason for that is this way I could hold the cake while wearing latex gloves whenever I needed to steady it (obviously I wasn’t driving the car) without marking the final icing layer.
Once at Monarto I whipped out a spatula and added the final luscious layer of vanilla icing. 
Then, just slice and serve! Woot!
It made for very looooong slices of cake. Unlike this photo, I took very thin slices and folded them in half to fit them on the cake. People loved the different flavours, especially the passionfruit.
We filled everyone up and send many home with extra cake for dessert!
We applied glitter tattoos to the guests instead of giving out party bags, which went down very well. Our one major oversight was not realising that there are no BBQ’s at Monarto Zoo. The very kind café owner came to our rescue and cooked up all our sausages for our lunch for everyone. We were so lucky! Rose had a great day and the next day I took her back there to feed the lions. It was a really awesome weekend. 😀
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