1. CREAM together the butter and sugar until light and fluffy. Add the eggs and vanilla and beat well. Fold in the flour alternately with the milk. Divide the mixture into 3 bowls; add the cocoa and extra milk to one and the pink food colouring to another.
2. PLACE alternate spoonfuls of mixture into a greased and lined 20cm round cake pan. Use a knife to swirl the mixture into a marble effect.
3. BAKE in a moderate oven 180°C for 45 minutes or until cooked when tested. Cool on a wire rack for 10 minutes before turning out of pan to cool completely.
4. SIFT together the icing sugar and extra cocoa. Stir in the butter and enough hot water to make a thick icing. Ice the cake and decorate with sprinkles .Store in an airtight container until required.