Instructions

1. 1
   Preheat the oven to . Grease and line six round cake tins.
2. 2
   Beat the butter, sugar and vanilla in a large mixing bowl, until soft and fluffy.
3. 3
   Beat in the eggs, two at a time.
4. 4
   Combine the flour and baking powder. Fold this dry mixture into the batter.
5. 5
   Divide the mixture into 6 separate bowls.
6. 6
   Add the red food colouring, one drop at a time, to the mixture in one bowl and stir in until the mixture reached the desired colour.
7. 7
   Repeat step 6, using orange, yellow, green, blue and purple food colourings.
8. 8
   Spread the red mixture in one of cake tin. Repeat with other colours.
9. 9
   Bake for 25 minutes, in batches of two cakes, until a skewer inserted comes out clean.
10. 10
    Transfer the cakes to a wire rack and leave to cool. Unmold cakes.
11. 11
    For the icing, beat the butter in a mixing bowl until soft.
12. 12
    Add half of the icing sugar, 1 cup at a time, and beat in.
13. 13
    Beat in the milk and vanilla extract.
14. 14
    Add the rest of icing sugar, 1 cup at a time, and beat in.
15. 15
    Spread one-eighth of the icing onto the purple cake. Top with blue cake layer, and press gently.
16. 16
    Repeat the frosting and cake layering in rainbow order, finishing with the red layer.
17. 17
    Spread the rest of icing all over the cake.
18. 18
    If you like, sprinkle the cake with sprinkles.
19. 19
    Enjoy!