Better tomato sauce, with an onion and butter base

2 lb. fresh, ripe tomatoes, prepared via blanching and peeling, OR 2 cups canned imported Italian plum tomatoes, cut up, with their juice
5 tablespoons butter
1 medium onion, peeled and cut in half
Salt
1 to 1.5 pounds pasta
Freshly grated parmigiano-reggiano cheese for the table

Put either the prepared fresh or canned tomatoes in a saucepan.
Add the butter, onion, and salt.
Cook uncovered at a very slow, but steady simmer for 45 minutes or until the fat floats free from the tomato. Stir from time to time, mashing any large piece of tomato in the pan with the back of a wooden spoon.
Taste and correct for salt.
Discard the onion before tossing the sauce with pasta.
You can freeze the sauce when you're done; just discard the onion first.