In a large bowl, crush the whole tomatoes with your fingers to form a course puree.
Stir in the tomato paste, salt, pepper flakes, sugar, basil, and parsley, and set aside.
In a large saucepan, heat the olive oil over medium heat. Add the onions and cook for 5 minutes, stirring often, until the onions begin to soften.
Add the garlic and cook, stirring often, for 2 minutes (do not brown the garlic).
Add the tomato mixture, and simmer over medium-low heat for 30 minutes, stirring occasionally.
Taste and adjust seasoning.
When sauce is almost complete, and pasta is boiling, remove 1/2 cup of starchy pasta cooking water and add it to sauce, bring to a gentle boil, and let sauce emulsify and thicken for about 5 minutes.
Serve over pasta and enjoy.