Bring a large pot of water to a boil. Fill a large bowl with ice water.
Make an X with a sharp knife on the bottom end of each of the tomatoes. Drop the tomatoes into the boiling water, cook for 60 seconds, then remove with a slotted spoon to the ice water. Let cool for a minute or two.
Place the tomatoes on a cutting board with a groove to catch the juices, and dump out the ice water, reserving the bowl. Peel off the tomato skins, then roughly chop the tomatoes, discarding the stems and any white cores. Transfer the chopped tomatoes to the bowl with all of the juices.
Meanwhile, return the same pot that you cooked the tomatoes in to the stove over medium heat. Add the olive oil, then add the garlic and onions and sauté, not allowing the garlic and onions to get more than lightly golden (about 5 minutes, until soft). Stir in the red pepper flakes, if using, and season with salt and pepper. Add the tomatoes and all of their juices, and turn the heat up to high. Bring to a simmer, add the sugar, and cook for about 10 to 20 minutes until the sauce is as thick as you like it. Stir in the fresh herbs. Check and adjust the seasoning.
While the tomato sauce finishes cooking, cook the pasta in a large pot of salted water according to package instructions. At this point, if you like a chunky sauce, you can simply drain the pasta, return it to the pot, and toss it with the sauce to combine. Or you can use an immersion blender to puree the sauce as smooth as you’d like right in the pot, or carefully transfer it to a food processor or blender and pulse or puree the mixture — in batches if necessary — until it reaches the desired consistency.
Serve in a large shallow serving bowl, or in individual bowls. Pass the Parmesan for those who want it.
Notes
If you have a food mill and plan to put the sauce through the mill when it is cooked, you can skip blanching the tomatoes; the food mill will prevent the skins from going through into the sauce. As for the seeds and the juice, just let the whole tomato be part of the sauce — no need to seed.
You can cook the tomatoes for as little or as long as you want, and you’ll still have a lovely clean sauce. The longer you cook the sauce, the thicker and more concentrated it will get.
If you have the opportunity to mix different varieties of tomatoes, then you’ll get a blend of different notes of sweetness and acidity.
If you prefer a chunky, rustic sauce, just skip the blending step altogether.