Step 1In plenty of rapidly boiling salted water, briefly cook the tomatoes just until the skins loosen, 10 to 15 seconds. Drain the tomatoes and rinse under cold water. Peel them, cut them in half crosswise and squeeze out the seeds and water. Chop them coarsely and place them in a wide serving bowl with the basil, and cover with the oil.
Step 2Cook the spaghetti in the same water until al dente, about 9 minutes, drain it and add to the tomatoes. Stir them together roughly until the mixture is cool. Season to taste with salt and pepper and stir in a tablespoon of the cooking water.