Tomato Sauce w Butter and Onions by ​Marcella Hazan​

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. Before tossing with pasta, you may remove the onion (as Hazan recommended) and save for another use, but many opt to leave it in. Serve with freshly grated parmigiano-reggiano cheese for the table.

​2 pounds fresh, ripe tomatoes, blanched and peeled, 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