To prepare the artichokes first slice off the top third of the leaves and cut off the stems. Cook, uncovered, in a large saucepan of boiling salted water for about 30 minutes. To test if they are done scoop one out of the water with a slotted spoon. Pull at a bottom leaf and if it comes away cleanly they are ready. Remove the artichokes from the pan and leave to drain welll, upside down, then keep warm.