From WP. It didn't explain why this is called "III". I've run across several tomato sauces that simply use tomatoes, an onion (not diced just cut in half) and a lot of butter. In some ways this is similar to my roasted tomato sauce recipe, which uses a lot of olive oil instead of a lot of butter.
Ingredients
Scant 2 pounds fresh, ripe Roma tomatoes (may substitute 28-ounce can peeled whole San Marzano tomatoes; see NOTE)
8 tablespoons (1 stick) unsalted butter
1 medium onion, cut lengthwise in half
Salt
1 teaspoon sugar (optional)
Instructions
1. If using fresh tomatoes: cut the fresh tomatoes in half lengthwise. Place them cut side down in a wide saucepan; cover and cook over medium-low heat for 10 minutes, until slightly softened. Working in batches as needed, transfer the tomatoes to a hand-cranked food mill set over a mixing bowl. Puree until the solids are completely broken down, with tomato seeds and skins left in the mill. Discard the solids; pour the pureed tomatoes and juices back into the saucepan. Proceed with step 3.
2. If using canned tomatoes, puree, chop or squish them and pour into saucepan.
3. Add the butter and onion halves, cut sides down. Cook over medium heat until the butter has melted, then season lightly with salt and add the sugar, if using.
4. Reduce the heat to medium-low; cook (uncovered) for about 45 minutes, stirring occasionally, to form a smooth, brightly colored sauce that has thickened a bit.
5. Taste, and season with salt, if desired. Discard the onion before serving or storing.