In a large pot, heat the olive oil over medium heat. Add the finely diced onion and sauté until translucent, about 5 minutes.
Once the onions are soft, add the minced garlic to the pot and cook for an additional minute.
Pour in the crushed tomatoes and diced tomatoes. Stir well to combine.
Add the tomato paste, Italian seasoning, salt, black pepper, and crushed red pepper. Stir until well mixed.
Taste the sauce and adjust the sweetness by adding sugar as needed.
Reduce the heat to low and let the sauce simmer uncovered for about 20-30 minutes.
Just before serving, stir in the fresh basil for added flavor.
