Rainbow drip cake

Method

1. Preheat the oven to 180°C/fan 160°C/Gas 4
2. Grease and line all 6 cake tins
3. For the 20cm base tier, whisk 400g of the butter and 400g of the sugar together using an electric whisk until light and fluffy. Add 6 eggs, one at a time, whisking well after each addition, then sift in 400g of the flour and 1/2 tsp of the salt
4. Fold with a large spoon until just combined
5. Stir in 60ml of the milk and 11/2 tsp of the vanilla extract, then weigh the whole mixture
6. Divide the weight by 3 and spoon each third into a separate bowl
7. Add one each of the purple, blue or green food colourings to each bowl, until you reach your required intensity of colour
8. Transfer to the 3 x 20cm tins and bake in the oven for 25-30 mins, or until a skewer inserted into the centre comes out clean
9. Leave the cakes to cool in their tins for 5 mins before turning out to cool completely
10. Meanwhile follow the steps again to make the sponge for the 15cm top tier – using 200g butter, 200g sugar, 3 eggs, 200g flour, 1/4 tsp salt, 30ml milk and 1 tsp vanilla extract
11. This time, use the yellow, orange and red food colourings
12. Once all the cakes are cool, use a serrated knife to trim the tops to make the cakes level
13. Lightly trim or scrape away any discoloured edges too
14. Next, make the cream cheese icing
15. Whisk the butter and icing sugar together until light and fluffy
16. Gradually add the cream cheese a spoonful at a time, whisking until combined
17. Add the vanilla extract and whisk for 1 more minute
18. Sandwich the 3 x 20cm sponges together using a few tablespoons of the icing between each layer
19. Start with the purple sponge, then the blue, then the green
20. Separately sandwich the yellow, orange and red sponges together so the red is at the top
21. Cover both cakes completely with the remaining icing, using a pallet knife or icing scraper to create a smooth surface
22. Leave to set in the fridge for 1 hour before decorating
23. For the drizzle icing, put the icing sugar in a bowl and add the beaten egg white and lemon juice
24. Whisk on a low speed for 2-3 mins until you have a smooth, stiff-peak consistency
25. Stir in 1 tbsp cold water until you have a thick but just runny icing that will dribble slowly down the cake
26. Test on a plate to see how quickly it dribbles, and add 1-2 tsp more water if needed
27. Divide between 6 bowls and add a little food colouring to each, then spoon into piping bags
28. Take the cakes out of the fridge and put the small one on the top of the larger one
29. Use the hundreds and thousands to create a band around the bottom tier
30. Then, using a skewer or knife, lightly indent the top tier to make marks where the colour wheel will go – you'll need 12 wedge shapes
31. Use the piping bags to pipe the wedges (in the order purple, blue, green, yellow, orange and red) round the cake twice
32. Finally, gently encourage dribbles to come down the sides of the top tier and begin dribbling down the second tier
33. Leave to set