Preheat oven to 180C. Cream ½ cup butter with sugar until light and fluffy. Add ¼ cup cocoa and one teaspoon vanilla essence. Mix well then add eggs and combine. Add half the flour and bicarbonate of soda and mix well. Add ½ cup boiling water and mix well. Repeat with remaining flour, bicarbonate and ½ cup water.

The mixture will be quite runny. Pour into a greased and bottom-lined 20cm round or square cake tin. Bake for 45-50 minutes, until risen and cooked when tested with a skewer. Remove from oven and cool on wire rack.

To make chocolate icing, beat remaining butter and vanilla essence, then gradually add icing sugar and beat until light and fluffy. Mix remaining cocoa with three tablespoons boiling water then add to mixture and beat until well combined. Spread over cooled cake.