Dice onion and set aside.
Dice garlic and set aside.
Heat large pot over medium low heat and add oil.
Add onion and sauté for 5 minutes until onion is translucent.
Add garlic and sauté for 1 minute.
Add canned tomatoes, tomato paste, tomato sauce, Italian seasoning, red pepper flakes, and salt & pepper.
Bring to boil and reduce to simmer.
Cover and simmer for 15 minutes.
Using an immersion blender, blend sauce to break up tomatoes and onion for 2 minutes. If you do not have an immersion blender, transfer liquid to blender and blend.
Blend sauce until desired smoothness.
Add fresh basil with sauce and serve or freeze.