most famous and buttery tomato sauce

I made this last night and it was very tasty--like tomato butter.   

 from Marcella Hazan's Essentials of Classic Italian Cooking.

Serves 2, enough to sauce 1 to 1 1/2 pounds pasta

For the Sauce:

• 2 pounds (about 5 midsize tomaties) fresh, ripe tomatoes, prepared as described below, or 2 cups canned imported Italian tomatoes, cut up, with their juice Ask a question about this ingredient.
• 5 tablespoons butter!!! Ask a question about this ingredient.
• 1 medium onion, peeled and cut in half Ask a question about this ingredient.
• Salt to taste Ask a question about this ingredient.

1. 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. Ask a question about this step.
2. Stir from time to time, mashing up any large pieces of tomato with the back of a wooden spoon. Ask a question about this step.
3. Taste and correct for salt. Discard the onion before tossing with pasta. Serve with freshly grated parmigiano-reggiano cheese for the table.  
 

via food52.com