Heat the olive oil in a large saucepan over medium-low heat.
Add the chopped onion and cook, stirring frequently, until soft and golden, about 5–7 minutes.
Add the minced garlic and cook, stirring, until fragrant and lightly golden, about 30–60 seconds; avoid burning the garlic.
Stir in the basil, parsley flakes, ground black pepper, oregano, and salt.
Add the crushed tomatoes, tomato puree, and sugar, then increase heat to medium-high and bring the sauce to a boil.
Reduce heat to low, cover loosely, and simmer for 30 minutes, stirring occasionally.