So, judging by the reaction I’ve had every time I’ve shown anyone any photos of this cake, this is probably the first recipe I ought to be sharing. Because, let’s face it, that was one spectacular-looking cake.
It’s also a lot easier than it looks. Seriously, if you can make a passable marble cake, and have access to good-quality food colouring, you can make this.
I actually found the prototype for this recipe online, and I’ll share the YouTube video below, because I didn’t actually take photos of the various steps, being as I was engaged in just trying to get the thing to work.
I changed a handful of things for this recipe. For one thing, I made it gluten-free, using a modified version of my gluten-free flour mix. For another, I decided to flavour it with orange flower water instead of vanilla. Using orange blossoms in the bouquet or bridal wreath is a very old bridal tradition, and I thought it would be nice to give a nod to that, especially given how interested one of the brides had been in my use of rosewater and lavender in cupcakes. I kept the flavour pretty subtle, because too much orange flower water can be very much like eating soap.
But you know what was the big thing I did that changed this cake into a proper rainbow cake?
I baked it in a smaller tin.
And the smaller tin meant that the arch of the rainbow was raised, giving a much more impressive rainbow effect than it might otherwise have had.
I’m going to suggest two different decorating ideas for this – the one I used in my practice run, and the one I used for the actual wedding cake. It really depends how formal you are feeling…
Your shopping list
270g gluten-free flour mix
3 tsp baking powder
½ tsp salt
1 tsp orange flower water
red, yellow, green, blue and purple food colouring pastes (these are far more vibrant than liquid food colouring)
200g white chocolate
65 ml cream
500g white icing OR lots of hundreds and thousands
You will also need a 5 inch (12.5cm) round tin with tall sides.
Now what will you do with it?
Grease the tin with butter, and line the bottom and the sides. You really don’t want all your good work to come to nothing when you turn the cake out! Preheat oven to 170°C.
(Also, you need to know now that you are not going to use all this mixture in a cake tin this size. You need somewhere between 2/3 and 3/4. You can make the rest into really psychedelic cupcakes, if you want.)
Cream the butter and the sugar, then beat in the eggs one by one.
Beat in the dry ingredients, then the yoghurt and the milk. Mix in half a teaspoon of orange flower water, and taste to see if it’s strong enough. Add the other half teaspoon if you think it needs more (I’ve found that some brands are stronger than others).
Divide the mixture between six bowls, and colour them red, orange, yellow, green, blue and purple. Orange requires only a tiny amount of red compared to yellow, and I strongly recommend that you buy a purple colour if you can – you can never get a really vibrant purple from red and blue colour.
Make sure the mixture is super-bright. Now is not the time to worry about the chemicals in food colouring – you don’t want a pastel rainbow, and baking will bleach the cake slightly.
Now for the fun bit! Get a big dollop of the red mixture – about 2/3 – 3/4 of what’s in the bowl, and plop it carefully into the middle of the tin. Bang the tin really hard on the bench to make the red mixture spread out a bit. It won’t go all the way to the edges yet, and that’s fine.
Get a similarly sized dollop of the orange, and plop it carefully into the very centre of the tin on top of the red. Bash the tin on the bench again – the orange will spread out with the red spreading out further under it, so you have concentric circles. Well, circle-ish things.
If this is confusing, have a look at the video below. This is where I got the recipe from – so thank you Emma, for this fantastic method.
Dollop the yellow on top of the orange, and repeat the banging bit, then do the same with the green, then the blue, then the purple.
If you are miraculously good at this, you should be able to see a little bit of red, a little bit of orange, a little bit of yellow, a little bit of green and a little bit of blue, all in concentric circles under the purple. I wasn’t that good, but it still worked pretty well.
If you are about 2/3 of the way up the tin, you can stop here. If it’s only half full, go for a double rainbow. The next layers will be a bit smaller, but that’s OK.
Put the tin in the oven, and bake for about 45 minutes to an hour. If, after 45 minutes, it’s browning too fast but still wet in the middle, reduce the temperature to 165. It will bake eventually, I promise, but deep cakes are a bit tricky. This one should pass the skewer test when it’s done.
Turn the cake out onto a wire rack to cool.
Once the cake is cool, your next step is to make the cake nice and flat on top, because you want to serve this cake upside down from where it was in the tin, so that you have a rainbow rather than a series of colourful smiles. I have no tips for this. My cakes almost always turn out looking drunk. I fluked the wedding cake, and it was still a tiny bit crooked, frankly. Just do your best.
Now you are going to cover the cake in ganache and then either white icing, or sprinkles.
To make the ganache, chop the white chocolate finely and put it into a bowl.
Bring the cream to a boil, and pour over the ganache. Cover the bowl with a lid for a minute or so, to start the chocolate melting, then stir the mixture until it is smooth. Use a spatula to coat the cake thinly in ganache.
If you are looking for a nice, formal cake, you want the white icing. Sprinkle your work surface with icing sugar, and knead the icing firmly until it is soft enough to work into a smooth ball.
Use a rolling pin to roll it out. It wants to stick to the surface, so what you do is this. First, sprinkle more icing sugar on the work surface, and roll the rolling pin over the ball twice, away from you, so that you have an oval. Pick it up, and turn it over, and then rotate it 90 degrees and roll the rolling pin over it twice more. Turn it over and rotate it again, and keep going until the icing is about 3-5 mm thick, and big enough to cover the cake with several centimetres to spare on each side. So about 35cm diameter, maybe? The reason you are turning it over constantly, by the way, is that this helps the icing not to stick to the work surface, so don’t forget to do that bit.
Now you need to drape it over the cake. This is a pain, and the trick is not to stretch it. Pick it up carefully and place it gently over the top of the cake. Use a spatula or smoother (or your hand…) to smooth down the top of the cake only.
Now smooth the cake down the sides with downward strokes, a little at a time. If you are about to get wrinkles, gently pull the bottom of the icing outward, being careful not to stretch it, while you smooth down the side from top to bottom. If you are lucky, this will result in no lumps or wrinkles. I strongly suggest watching some YouTube videos (look up ‘covering a cake with fondant’) until you think you can replicate the method. That’s what I did…
If this sounds like way too much faffing around, go with the sprinkle topping instead!
To do this, cover the cake with ganache again, but this time, get out a big metal skewer and skewer the cake from bottom to top.
Make a layer of 100s and 1000s or other coloured sprinkles on a long, flat tray or your working surface, and use the skewer to place the cake on its side at one end of the sprinkles. Carefully push the skewer all the way through the cake, and use it to roll the cake along the layer of sprinkles until it is completely coated.
Now draw back the skewer a little, and use it to lever up the cake and place it face down into the sprinkles (or alternatively, get the cake back onto a cake plate, and leave the top white, or cover it with sprinkles by the more traditional, sprinkling method).
Carefully lever the cake up onto a cake plate.
Serve to someone who needs more colour in their life!
This is a gluten-free cake, obviously, and it is also low in fructose, and nut-free. You could probably make a vegan version – just start with a vegan cake recipe that has a fairly wet, but not liquid, consistency. You don’t want something that is too pancake-batterish, but you don’t want something really stiff, either. I’m sorry – I don’t have any recommendations for this one.
If you just need it to be gluten and dairy free, you can, of course, use a good dairy-free margarine like Nuttelex, and a soy or coconut milk and yoghurt.
I’m sure you could use natural food colours for this, but I think you’d have to work hard to stop your rainbow from being too pastel – though that could be pretty, too, in the right circumstances.