1. Gather all ingredients: high-quality canned San Marzano tomatoes, onion, garlic, oregano, basil, and olive oil.
2. Crush the canned tomatoes by hand in a bowl and set aside.
3. Heat olive oil in a wide skillet or saucepan over medium heat.
4. Start with cold oil and add minced garlic to prevent burning.
5. Sauté chopped onions and garlic until softened and fragrant.
6. Stir in dried oregano and cook for a few seconds to release its flavor.
7. Add the hand-crushed tomatoes to the skillet and stir well.
8. Simmer uncovered for about 20 minutes to allow the sauce to thicken.
9. Stir occasionally and adjust heat as needed to prevent scorching.
10. If desired, add optional ingredients like red pepper flakes, tomato paste, or a Parmesan rind.
11. Taste the sauce and adjust seasoning with salt and pepper if needed.
12. Stir in fresh basil just before removing from heat.
13. Let the sauce cool slightly before using it for pasta, pizza, or casseroles.
14. Store leftovers in the fridge for up to a week or freeze for up to six months.
15. Enjoy a fresh, homemade marinara sauce that is healthier and free from preservatives.