2 pounds fresh, ripe tomatoes, prepared as described below, or 2 cups canned imported Italian tomatoes, cut up, with their juice
5 tablespoons butter
1 medium onion, peeled and cut in half
Salt to taste
Put either the prepared fresh tomatoes or the canned in a saucepan, add the butter, onion, and salt, and cook uncovered at a very slow, but steady simmer for about 45 minutes, or until it is thickened to your liking and the fat floats free from the tomato. Stir from time to time, mashing up any large pieces of tomato with the back of a wooden spoon. Taste and correct for salt. Discard the onion before tossing with pasta. Serve with freshly grated parmigiano-reggiano cheese for the table.
Making Fresh Tomatoes Ready for Sauce
fresh, ripe plum tomatoes (or other varieties, if they are equally ripe and truly fruity, not watery)
The blanching method: Plunge the tomatoes in boiling water for a minute or less. Drain them and, as soon as they are cool enough to handle, skin them, and cut them into coarse pieces.
The freezing method (from David Tanis, via The Kitchn): Freeze tomatoes on a baking sheet until hard. Thaw again, either on the counter or under running water. Skin them and cut them into coarse pieces. The food mill method: Wash the tomatoes in cold water, cut them lengthwise in half, and put them in a covered saucepan. Turn on the heat to medium and cook for 10 minutes. Set a food mill fitted with the disk with the largest holes over a bowl. Transfer the tomatoes with any of their juices to the mill and puree.