Ingredients

For the cake:
600g local unsalted butter, softened
600g caster sugar
9 large free range eggs, lightly beaten
600g self raising flour, sifted, plus extra for dusting
¾ tsp salt
90ml local milk, semi skimmed/reduced fat
2½ tsp vanilla extract
Food colouring (purple, blue, green, yellow, orange and red)

For the cream cheese icing:
600g local unsalted butter, softened
750g icing sugar
600g full fat cream cheese
1 tsp vanilla extract

For the drizzle icing:
200g icing sugar, sifted
1 large egg white, lightly beaten
½ tsp lemon juice
Food colouring (purple, blue, green, yellow, orange and red)
1 pack Hundreds and Thousands/sprinkles

You will need:
6 clean piping bags
3x 20cm cake tins
3 x 15cm cake tins
1 pallet knife or icing scraper

Method

Preheat the oven to 180°C/fan 160°C/Gas 4

Grease and line all 6 cake tins

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

Fold with a large spoon until just combined

Stir in 60ml of the milk and 1½ tsp of the vanilla extract, then weigh the whole mixture

Divide the weight by 3 and spoon each third into a separate bowl

Add one each of the purple, blue or green food colourings to each bowl, until you reach your required intensity of colour

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

Leave the cakes to cool in their tins for 5 mins before turning out to cool completely

Meanwhile follow the steps again to make the sponge for the 15cm top tier – using 200g butter, 200g sugar, 3 eggs, 200g flour, ¼ tsp salt, 30ml milk and 1 tsp vanilla extract

This time, use the yellow, orange and red food colourings

Once all the cakes are cool, use a serrated knife to trim the tops to make the cakes level

Lightly trim or scrape away any discoloured edges too

Next, make the cream cheese icing
Whisk the butter and icing sugar together until light and fluffy

Gradually add the cream cheese a spoonful at a time, whisking until combined
Add 1 tsp of vanilla extract and whisk for 1 more minute

Sandwich the 3 x 20cm sponges together using a few tablespoons of the icing between each layer

Start with the purple sponge, then the blue, then the green

Separately sandwich the yellow, orange and red sponges together so the red is at the top

Cover both cakes completely with the remaining icing, using a pallet knife or icing scraper to create a smooth surface

Leave to set in the fridge for 1 hour before decorating

For the drizzle icing, put the icing sugar in a bowl and add the beaten egg white and lemon juice

Whisk on a low speed for 2-3 mins until you have a smooth, stiff-peak consistency

Stir in 1 tbsp cold water until you have a thick but just runny icing that will dribble slowly down the cake

Test on a plate to see how quickly it dribbles, and add 1-2 tsp more water if needed

Divide between 6 bowls and add a little food colouring to each, then spoon into piping bags
Take the cakes out of the fridge and put the small one on the top of the larger one

Use the hundreds and thousands to create a band around the bottom tier

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

Use the piping bags to pipe the wedges (in the order purple, blue, green, yellow, orange and red) round the cake twice

Finally, gently encourage dribbles to come down the sides of the top tier and begin dribbling down the second tier

Leave to set, then enjoy!