Pour the oil in a large pot over medium heat.
1/4 cup (60 ml) olive oil
Stir in the onion and continue cooking, stirring often, until the onion is soft. This takes about 5 minutes.
1 cup (145 grams) onion
Add the garlic and cook, stirring often, another 1 minute.
3 tablespoons fresh garlic
Pour in the full contents of the cans and use a wooden spoon to break the tomatoes into pieces.
56 ounces canned whole tomatoes
Add the remaining ingredients. Cover and bring to a boil, stirring occasionally.
2 teaspoons dried oregano, 1/4 teaspoon red pepper flakes, 1 1/2 teaspoons salt, 1/4 teaspoon ground black pepper, 20 basil leaves
Turn the heat down to keep it at a simmer. Simmer, uncovered, for about 10-15 minutes.
Let cool completely. Store in an airtight container in the fridge for up to 5 days. It can also be frozen for several months.