For his birthday Adam has asked for a rainbow cake covered in plain white sugarpaste that he can draw on with edible pens (like this one from Sweetapolita) and even though his birthday isn't until July I thought I should have a go at making it now so I have time to tweak the recipe if needed.
The recipe I used was originally a three layer chocolate cake, but I replaced the cocoa powder with extra flour and split the finished mixture into 6 parts rather than three. I've found that the most accurate way of doing this is to weigh the mixing bowl before you start, then again when you've added all the ingredients. Simply take away the original weight of the bowl and divide by as many layers as you want. In my case it worked out to 138 grams per layer. Once you've got the cake mix divided into separate bowls just add a different food colour to each bowl. For this to work properly you have to use the paste or gel food colours. The liquid ones are too runny to get a really vibrant colour. The ones I used were Sugarflair colours.
|Tangerine and Christmas Red|
|Melon and Party Green|
|Ice Blue and Grape Violet|
The colours of the cake mix will be pretty much the colour of the finished cake so make sure it's as bright as you want it.
100g dairy free margarine (at room temp)
260g caster sugar
1/4 teaspoon vanilla extract
3/4 teaspoon baking powder
3/4 teaspoon bicarbonate of soda (baking soda)
a pinch of salt
215g plain flour
160ml rice milk or other dairy free milk
20cm (8 inch) round shallow tins, greased and bases lined
Preheat your oven. I set mine at Gas Mark 3 (170C or 325F), but because the layers were so thin I think it probably should have been GM 2 (150C or 300F) and baked for a bit longer. Remember to weigh your bowl before you start too, it makes separating the mix so much easier.
Cream together the butter and sugar. Beat it on a fairly high speed for about 5 minutes until it's light and fluffy; it may take a minute or so longer as it's margarine instead of butter.
Add the eggs one at a time, beating thoroughly after each.
Turn your mixer down to slow and add the vanilla extract , 45 grams of the flour, the baking powder, bicarbonate of soda, and the salt and beat until well mixed. If you try and do this with the mixer still on high you will end up with a fine film of flour over everything in your kitchen. Trust me on this, turn the mixer down!
Add half of the remaining flour, all of the milk, then the last of the flour. Mix well until everything is combined.
Now you've reached the fun part! Weigh out your mix into six bowls (you did remember to weigh the mixing bowl before you started, right?) and colour each bowl differently. Add each colour to a different tin (I only had two tins so I had to do mine in batches) and bake in the oven for 25 - 30 minutes. I baked mine two layers at a time, one on the middle shelf and one below it but off to one side. Once the top tin finished I moved the bottom tin up a shelf and had to bake for a further ten minutes or so. Bear in mind that once they're baked the outside of the cake layers might look a bit ... funky. Don't worry, the inside of the layers will be the correct colours!
Once all the layers are baked and cooled it's time to assemble your cake! I used a really simple buttercream icing for mine (125 grams dairy free margarine, add 400 grams icing sugar and beat well. Add 1 teaspoon of vanilla extract, beat until smooth and creamy) It's a slightly off-white colour because of the margarine, but it would probably work fine if you replaced the margarine with vegetable shortening. I needed two batches of this icing, one for between the layers and a crumb coat and one for the top coat and swirls. I probably have far too much on though because I actually ran out of icing towards the end.
For the outer layer of icing I added a little more on top on the crumb coat and then used a number 8 PME star nozzle to pipe swirls all over the cake.
I did have some problems with this cake. The layers were very thin, so they went rather hard and crispy round the edges and I ended up having to trim them. I think next time I make this I'll use one and a half times the recipe, or possibly even double it. If I double it, I'll keep the temperature at GM3, but for one and a half I'd probably turn it down to GM 2 and bake for a bit longer.
The important thing is that it tasted great, crispy bits and all, and Adam is already looking forward to his birthday cake!