Skin, seed and dice the tomatoes: bring a saucepan of water to the boil. Fill a bowl with cold water and set aside. Remove the stems from the tomatoes and make a shallow, cross-shaped incision in the opposite ends. Gently lower the tomatoes into the boiling water for about 10 seconds. Remove with a slotted spoon and drop immediately into the bowl of cold water. Peel off the skins with a paring knife. Halve the tomatoes crosswise and squeeze gently to remove the seeds. Cut the flesh into 1 cm (1/4 inch) dice (this is known as tomate concassée).