Heat the oil in a medium large pot over medium heat. When the oil is shimmering, add the onion. Cook the onion for about 4 minutes, stirring often, or until the onion is translucent. Add the garlic and tomato paste and cook for another full minute, stirring constantly.
Add the tomatoes to the pot. Use a handheld potato masher or the back of a spoon to crush them (they'll spatter, so wear an apron!). Add the salt, sugar if using, and water. Allow the mixture to come to a vigorous simmer, then turn the heat to low. Throw in a handful of fresh herbs, if desired. Simmer, uncovered, for ten minutes, or until the sauce has thickened.
At this point, you can add cooked pasta directly to the pot (you'll need about 12oz/340g pasta) for a pasta supper, or you can transfer the sauce to an airtight storage container. Store in the fridge for up to 5 days or freeze for up to 6 weeks.