Step 1

Preparation If using fresh tomatoes, peel them. Coarsely chop the fresh or canned tomatoes. Trim both ends of the onion; peel it and cut it in half lengthwise.

Step 2

Put the tomatoes, onion, butter, and salt in a 4- to 5-quart saucepan over medium heat. When the tomatoes begin to bubble, lower the heat to a slow but steady simmer. Cook, stirring every 10 to 15 minutes, until the tomatoes are no longer watery and the sauce has reduced, about 45 minutes, depending on the size and shape of the pot. The sauce is done when the butter has separated from the tomatoes and there is no remaining liquid.

Step 3

Cooks' NoteWhen you toss pasta with the sauce, add about 1/3 cup freshly grated Parmigiano-Reggiano.

Step 4

From Hazan Family Favorites: Beloved Italian Recipes by Guiliano Hazan. Copyright © 2012 Giuliano Hazan; photographs copyright © 2012 Joseph De Leo. Published by Stewart, Tabori & Chang, an imprint of ABRAMS.