Prepare the Tomato Sauce:
In a large saucepan, lightly heat oil. Add the garlic, oregano, and chili flakes and stir. Cook until the garlic softens and begins to change colour. Do not brown the garlic or it will burn. (If you prefer, you can slice the garlic, cook in the oil, and then remove after it has softened.)
Carefully add the passata.
Stir in salt and add basil. Bring to a boil and then reduce heat to medium.
Allow to simmer, stirring often for about 45 minutes. The sauce is cooked when it has reduced by about one-third and thickened. Taste and adjust salt if needed.