If your using whole canned plum tomatoes, place them in a bowl with their liquid and crush with your hands
Heat a frying pan on a medium heat. Pour in the oil and gently saute the onions until translucent (until they loose their color), then add the garlic and saute for a minute more taking care that the garlic does not burn.
Put in the bay leaf and fresh parsley, and/or basil, saute for a minute to help release the flavors from the spices.
Add the canned tomatoes, sugar, salt & pepper, bring to a simmer and cover.
Cook for 20 minutes stirring occasionally. Turn down the heat if you need to.
If the plum tomatoes were too watery, remove the lid, increase the heat and simmer gently for 5 minutes more to evaporate any excess water and thicken the sauce. If the sauce is too thick use a little warm water to thin it.