Rainbow layer cake - tutorial and recipe!

I LOVE rainbows, I've made a few of rainbow layer cakes and I always get asked for the recipe/method so I've finally written it down, including the recipe for the sponge and frosting - which is really yummy (so I'm told)

The pictures below are from 2 different ones I've made so that's why they don't quite match!

Rainbow cake

Ingredients for sponge:

560g caster sugar

480g plain flour

2 tbsp baking powder

½ tsp salt

4 eggs

280ml milk

160g unsalted butter (at room temp – softish)

1 tsp vanilla extract – or a bit of vanilla paste

Food colour gels/pastes – the concentrated ones, these can be found in Asda in separate pots or in other cake shops.

Ingredients for frosting:

750g icing sugar

240g unsalted butter (at room temp –softish)

75ml milk

1 tsp vanilla extract – or a bit of vanilla paste

Cake method:

1. Preheat oven to 180 degrees Celsius (less if fan assisted)

2. Put flour, sugar, butter, baking powder and salt into a bowl, mix until it resembles fine breadcrumbs – this can be done by hand or by using a hand mixer, just beware of the flour flying everywhere!

3. In a separate bowl or jug whisk together the eggs, milk and vanilla.

4. Add ¾ of the wet mix to the dry mix, mix together until just smooth, add the rest of the liquid and mix until incorporated –it’s important not to mix too much!

5. Divide the mix into bowls (depending on how many colours you are doing, 6 or 7 is about right for the mix ). I weigh mine because I'm anal like that!

6. Colour each bowl of mix a different colour.

7. Grease and flour 6 inch circle sandwich tins (I cook 2 at once).

8. Pour one colour into each tin.

9. Bake for about 20 minutes – checking each time that it is cooked all the way through.

10. Allow them to cool slightly before turning them out onto a plate to cool completely

Frosting method:

1. Mix all ingredients together with a spoon until the icing sugar is near enough incorporated.

2. Using a mixer mix beat it for as long as you can bare! I have a Kitchenaid stand mixer so my frosting gets 10 minutes on high and 5 on low, the longer you can manage the fluffier your frosting will be.

Once this is all done layer your cake putting some frosting in between each layer and then coat the whole of the outside of the cake with frosting  - then decorate with smarties etc if you wish. 

N.B I do what is called a 'crumb coat' (3rd picture down) where a very thin layer of frosting is spread all around to stick the crumbs to the cake - then the cake is put in the fridge for the frosting to harden (20 minutes ish). This makes it easier to get a smooth finish that doesn't have crumbs stuck in it. I also used straws to strengthen the cake as it was so tall it wobbled - I just poked them in so that they couldn't be seen, 4 per cake. This isn't essential!