Heat 2 tablespoons olive oil in a large saucepan over medium-low heat.
Add 1/2 cup chopped onion and cook, stirring frequently, until the onion is soft and golden, about 5–7 minutes.
Add 1 tablespoon minced garlic and cook, stirring, until fragrant and lightly golden, about 30–60 seconds; avoid burning the garlic.
Stir in basil, parsley flakes, ground black pepper, oregano, salt, and 4 tablespoons sugar until combined.
Add the 28 ounces crushed tomatoes and 29 ounces tomato purée; bring the mixture to a boil over medium-high heat.
Reduce heat to low, cover loosely, and simmer for 30 minutes, stirring occasionally.