Add the oil and lightly brown the onion in it.
Remove skin and seeds from the tomatoes and cut the flesh into quarters.
Finely chop the garlic; clean and prepare the peppers and cut them into strips.
Add the vegetables to the onion and simmer until all ingredients have combined to form a creamy sauce.
Season to taste with salt and pepper.
Note: This basic sauce, which provides the base for many stews and meat dishes, may also be prepared without the peppers.