Rainbow Cake Recipe

Thanks to my friend Simone who made Inigo’s first birthday cake, and then shared the recipe with me to make his second.

250 g butter
250 g white chocolate
200 mL water
1½ cups caster sugar
1¾ cups plain flour
1 cup self-raising flour
2 eggs, lightly beaten
½ cup sour cream
1 teaspoon vanilla essence

And food colouring. Don’t bother with the liquid ones you get at Woolies, you need specialty cake decorating gels. Liquid colours won’t give you the intense colours that you need for the full rainbow cake impact, and if you’re going to go to all that trouble, you want to get the wow factor. I got mine here – cheaper than eBay, and awesome quick service.

Preheat oven to 150°C. Line the cake pan with baking paper (this cake will stick).

Heat butter, sugar, chocolate, and water in a saucepan and stir over low heat until all combined. Let it cool a little bit so the self-raising flour doesn’t fizz before its time.

Sift both flours together and blend into chocolate mixture (don’t worry about lumps).

Stir in eggs, sour cream and vanilla (use a whisk for this bit and any remaining lumps will break up once these wet ingredients go in).

Pour the mixture into a deep 20 cm tin* and cook for about 1 hour, or pour into two 20 cm shallow tins and cook for about 45 minutes (this time is way out – cook it until a skewer comes out clean which will take much longer). I would also seriously consider cooking the cake/s au bain marie ie. once the mix has been poured into the cake pan, put the cake pan into a big roasting pan and fill the outer container with boiling water so the cake won’t form the really thick crust that comes with having to cook it for so long.

Recipe notes
Instead of sour cream you could use thickened cream, yoghurt or condensed milk, this just adds to the moistness of the cake. Also great with white chocolate ganache (hell, what isn’t?).


Here is where being married to a maths nerd is handy – but don’t worry, I married one so you don’t have to. My cake batter weighed at about 1600gms, so I separated out the batter for colouring in the following proportions –

500gms – red
400gms – orange
300gms – yellow
200gms – green
150gms – blue
50gms – violet

Pour the colours into the tin in the above order, trying as much as possible to keep the pouring centered. You will end up with a tin that looks like a multi coloured target from the top, and each colour will fall “inside” the previous colour like a bubble.

1.7 litres (3 pints) = 200 mm (8 in) ROUND = 180 mm (7 in) SQUARE
2.3 litres (4 pints) = 230 mm (9 in) ROUND = 200 mm (8 in) SQUARE
3.4 litres (6 pints) = 250 mm (10 in) ROUND = 230 mm (9 in) SQUARE
4.5 litres (8 pints) = 280 mm (11 in) ROUND = 250 mm (10 in) SQUARE

And if you want more rainbow goodness – try pancakes!

5 thoughts on “Rainbow Cake Recipe”

  1. Yay, I am so thrilled you have done all the hard work for me and I think I am definitely going to make this for Stella’s first birthday, its a winner! Lovely to meet you, thank you for the delicious biscuits!


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