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For the sponge
For the frosting
For the rainbow colours
Heat oven to 190C/170C fan/gas 5. Grease six 15cm sandwich tins and line them with one small disc of unbleached parchment paper or greaseproof paper. Make sure you’ve made the sides nice and greasy, you can use low fat cooking spray for this to keep the mess to a minimum.
Simply whizz up your beans in a blender and combine with all the other cake ingredients. divide the mix into 6 separate portions and add the different food supplement powders into each and mix. Place each different coloured mix into your pre greased pans and bake for 20-30 minutes until lightly golden. Alternatively bake the batches over 2 or 3 because really who has 6 cake tins to hand!
Let the cakes cool, then assemble one layer at a time, following the rainbow colours, adding a layer of frosting in between each layer of sponge (you will need about 1/3 to 1/2 the frosting at this stage). Use the remainder of your frosting to coat the sides and top of your cake and decorate with your favourite sprinkles. Let your cake set in the fridge for around 30 minutes prior to serving.
Other useful fruits and veggies for natural food colouring:
Red : tomato juice, paprika
Orange : carrot juice, cooked sweet potato, paprika
Yellow : saffron
Green : pistachio, spinach
Blue : red cabbage and baking soda
Purple : blueberries