To prepare the sauce, heat the olive oil in a large pan. Add the garlic and red chilli, cook for about 1 minute on a low heat, until soft. Add the tomato purée and cook for a further 1 minute.
Add the tomatoes and oregano and season with salt and pepper. Bring to a boil, reduce the heat and simmer for about 30 minutes, or until the sauce has thickened. Adjust the seasoning as necessary and add the basil.
The sauce will keep in the fridge for 1 week, and can be frozen for 3 months.
