Meanwhile cream together the butter and sugar until soft and fluffy. Add the beaten eggs a little at a time, making sure that they're completely incorporated after each addition. Add the vanilla and beat in then add the flour and mix to combine completely. Fold-in the milk to form a smooth batter and beat well.

Layer the sponge batter over the top of the syrup then cover the bowl with greaseproof paper and a double layer of foil. Tie securely then place in a steamer or on an inverted saucer placed in a large saucepan. Add boiling water 3/4 of the way up the pudding, cover and steam for about 90 minutes, or until the pudding is done through. Check the level of water every half hour and top-up with boiling water as needed.

Allow to cool in the bowl for a few minutes then unwrap the pudding and invert onto a serving plate (so that the syrup drips down the sides of the pudding). Serve immediately with hot custard.