Rainbow cake

Baked this cake for my grandson's 3rd birthday. His mum didn't have any special request and I have been wanting to try and make this cake for some time, so it was the perfect time to do it.

Didn't know which recipe to choose, so in the end used a sponge cake recipe. I had to double the quantity to get my 7 layers of the rainbow because I only had 3 tins, had to bake it 3 times to get the 7 layers.

Ingredients:
200 gm butter, softened
200 gm caster sugar
4 eggs, beaten
200 gm self raising flour
For the filling:
400 gm icing sugar
150 gm butter, softened
2 tsp single cream
For the icing:
500 gm icing sugar
a little water to bind the icing sugar

Method:
1. Preheat the oven to 180 deg C/Gas or 160 deg C/fn. Grease 2 deep 20cm sandwich cake tins. Line the base of each with greaseproof paper.*
2. Put the butter and sugar in a bowl and cream together until light and fluffy. Add the eggs a bit at a time, sprinkling in a bit of the flour to stop the mixture curdling. Sift and fold in the remaining flour. Divide the mixture into 4 bowls equally and add in your chosen colours.*
3. Then pour into baking tins and bake for about 15 mins then test with skewer. Leave the cakes in the tins for 5 mins, then turn out onto a wire rack and leave until cold.
4. Make your 2 batch of cake and repeat. You will have 1 extra layer - go on have that! :-)
5. While the cakes are cooling down, make the filling. Put all the ingredients into a bowl and beat with an electric mixer until smooth and fluffy, then use to sandwich all the layers together.
5. Make the icing. Sift the icing sugar into a bowl, then mix in 2-3 tbsps cold water to make a smooth icing. Pour the icing onto the top of the cake and quickly spread it over the top and sides. Leave the icing to set before serving.

Starting from bottom layer:
Violet, indigo, blue, green, yellow, orange and ending with red on top.