The most famous tomato sauce on the internet

from Marcella Hazan's Essentials of Classic Italian Cooking.
 For the Sauce:
 2 pounds fresh, ripe peeled tomatoes, 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.