It is said that this unusual pasta dish was invented by farmers in the backcountry of western Liguria, who had to cook their own lunch in the fields. Potable water was not always available, and only a limited amount could be carried over long distances, so these workers developed the technique of simmering their spaghetti directly in a sauce of fresh tomatoes —which they might have plucked right from the vine — with just a little water added.
In a large, heavy-bottomed pot, cook the onion, garlic, and pancetta or salt pork in oil over low heat for 20-30 minutes, or until onions are tender and translucent. Add tomatoes, salt and pepper to taste, and basil (if using). Stir well, cover, and cook for 40 minutes over low heat.
Add 2 cups water, mix in well, and then stir in pasta. Continue cooking, uncovered, over low heat, stirring frequently so that pasta doesn’t stick together. Add more water, ½ cup at a time, if necessary. Pasta should take about 30 minutes to cook, and sauce should reduce to a thick emulsion.
Serve with Parmigiano-Reggiano on the side.