This is one of Marcella Hazan's most famous and yet simple recipes, a recipe just like Livia would have made in The Wedding Officer.
Tomato Sauce from Marcella Hazan's Essentials of Classic Italian Cooking, as written on Cooking NYTimes
Yield: Sauce for 1 pound pasta
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 onion, peeled and cut in half
Salt to taste
Combine the tomatoes, their juices, the butter and the onion halves in a saucepan. Add a pinch or two of salt.
Place over medium heat and bring to a simmer. Cook, uncovered, for about 45 minutes. Stir occasionally, mashing any large pieces of tomato with a spoon. Add salt as needed.
Discard the onion before tossing the sauce with pasta. This recipe makes enough sauce for a pound of pasta.