Heat olive oil in a saucepan over medium heat
Sauté minced garlic (and diced onion, if using) until fragrant and softened
Add crushed tomatoes (and tomato paste, if using)
Stir in salt, black pepper, dried oregano, dried basil (or Italian seasoning), and red pepper flakes (optional)
Add a pinch of sugar (optional, to balance acidity)
Simmer uncovered 20–45 minutes, stirring occasionally
Add chopped fresh basil (optional) near the end
Taste and adjust seasoning
For a smoother sauce, blend briefly or crush with a spoon
Serve immediately or cool and refrigerate/freeze