Prepare the artichokes by washing them well and then trimming the sharp points from the leaves square with scissors. Cut off any stalk at the base to sit the artichoke level. Bring a large saucepan of water to the boil and add some salt. Cook the artichokes until tender. This depends upon the size. Generally you need to cook them for about 30 minutes. Test by seeing how easy it is to pull out a leaf. Now put under cold water to stop the cooking and set the colour. Pull out the centre leaves and remove the furry choke. Mix all the dressing ingredients together, adjusting to taste. Put an artichoke on a bed of fresh rosemary on a plate. Pour some of the dressing into the choke and serve the rest separately.