With a sharp knife, cut a small cross on the bottom of each tomato, then put them in a heatproof bowl and cover with boiling water. Leave for 30 seconds, then lift them out with a slotted spoon and put in a bowl of iced water. Lift the tomatoes out, then peel off and discard the skins. Cut the tomatoes into quarters, remove and discard the seeds, then roughly chop the flesh