Prehheat oven to 190°C and grease a (20x8in) cake tin.Making the dough:
Cream together butter and sugar in a bowl until light and fluffy.Gradually beat in the eggs and vanilla extract. In the unlikely case that the mixture starts to curdle, add a little of the flour.

Fold in the flour using a large wooden spoon, and carefully spoon mixture into separate bowls. The amount of bowls you use is depending on the amount of different colours you want in your cake.

Add selected food colourings to the bowls of cake mixture.

Making the cake:
Spoon the mixtures into the cake tin. Do a teaspoon of one colour, then another colour, then another colour. This gets the multi-coloured ‘rainbow’ effect.

Bake the cake for around 25 minutes, or until the whole cake is firm to the touch.

Note: The parts of the cake with the most colour will take longer to bake than the others.

Remove from oven and leave to cool for around five minutes before taking out of the tin and putting aside on a cool rack.

Making the icing:
Cream the butter in a bowl until smooth. Gradually mix in the icing sugar. When thoroughly mixed together, add just enough milk to make the icing fluffy and spreadable.