Bring a large pot of salted water to a boil. Drop the tomatoes, a few at a time, into the boiling water. Scald for 10 seconds, then with a slotted spoon transfer to a bowl of ice water. Scald all the tomatoes in this fashion, then drain, cool, and slip off the skins. Cut crosswise into halves, squeeze out the seeds and juice, and chop coarsely. Reserve.