Anyone who knows me knows I treat recipes as rough guides, but I’m happy to try to say what I did as best I can, though obviously your mileage may vary. I used this recipe http://speedbumpkitchen.com/rainbow-suprise-cake/ as a starting point.
To make big rainbow birthday cake (approx 40 adult portions):
- 5.5 cups self-raising flour
- 3 teaspoons baking soda
- 1 teaspoon salt
- 3 cups of sugar
- 4 cups soy milk
- 1.5 cups oil (I used sunflower but doubt it matters)
- 4 dessert spoons cider vinegar
- 2 dessert spoons vanilla bean paste. I used http://www.ocado.com/webshop/product/Taylor–Colledge-Vanilla-Bean-Paste/40798011?ULP_CAMPAIGN_ID=3&gclid=CM7A8oLa_8ECFUPLtAodTGcAIQ and I think it contributed positively to the cake texture.
- Sugarflair Sugarcraft Edible Blossom Tint Dusts in various colours. I got mine from the cake shop in the Covered Market in Oxford, but you can also buy online e.g. http://www.cakedecoratingstore.co.uk/sugarcraft-blossom-tint.html
For the icing:
I originally tried the half margarine, half shortening (vegetable suet) recipe as suggested on the speedbump kitchen site. It basically tasted exactly like Betty Crocker frosting, which is not my thing (which is why I didn’t do it for the Quiltbag cake), but may be yours. Instead I used:
- Approx 650g vegan margarine (eg Pure/Trex/Stork – whatever you can get hold of will do!)
- Approx 1.5kg of icing sugar
- 2 tablespoons vanilla
- Pinch of salt
- Splash (probably about 2 dessert spoons) of soy milk
- Jelly bean factory beans
- Co-op fondant
- Colours as above
Because I live in a charmingly ‘70’s house my oven is dodgy and I used gas mark “6”. I suspect it was more like 160/170 C on a normal fan oven though. Precision folks! 😛
To make the cake mix:
I mixed flour, baking powder, sugar and salt in a big bowl.
In a jug, I whisked together the milk, vinegar, oil and vanilla. This is meant to thicken/curdle and be gross! (don’t worry if you’re not used to it, it hasn’t gone horribly wrong). Then make a dip in the middle of the dry ingredients, pour in the wet ingredients and mix it all up. Magically you’ll have slightly bubbly cake mix.
I then measured out 400g of cake mix to make the first layer and coloured it by adding some blossom tint.
Put the cake mix in a lined tin and spread evenly over the base.
Bake for about 10/15 mins (until you have a nice cake smell in your kitchen and a pokey skewer comes out clean).
As I only have one pan and a tiny oven I did one layer at a time (I mentioned the 70s charm right?). So I washed up and mixed up the next colour as the previous one was in oven.
Once all the layers were done, I left them for an hour or so to cool.
Beat margarine until soft, with vanilla and salt.
Add icing sugar slowly until the marge has taken all it can and the mix is starting to get crumbly.
Then add the milk and beat until the buttercream is soft and the texture you want.
Compiling the cake
I buttercream-sandwiched the layers of cake in the (cool) pan that I had baked them in, to help guide the shape. The cakes shrunk as they cooled so they weren’t as big as the tin. To line them up, I positioned each layer flush against the bottom and one side. I put purple cake in the pan first, then buttercream, then blue cake, buttercream, green etc. (I’ve since discovered a traditional rainbow has red at the top so if you want to do that start with red at the bottom) I then put it in the fridge to set.
A few hours later, I trimmed off the wibbly edges and turned the firm cake stack out of the pan (purple now on top).
I then slooshed butter cream all over it with a palate knife and sprinkled jelly beans over it and put the fondant “1” I’d made in the middle.*
*Sorry, I can’t really describe how to make that beyond get some fondant icing and colour it (gloves are helpful to avoid colourful hands) and have a play.