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).