Heat the oil in a non-stick frying pan and fry the onions over a medium-low heat for 5 minutes until softened. Add the garlic, celery and carrots and cook for a further 5 minutes.
Add the tomatoes, breaking them up with a spoon. Add the bay leaves and tomato purée. Stir, cover and simmer for 15 minutes.
Season and add a little sugar, if you like, to bring out even more of a tomato flavour. Serve tossed into the cooked pasta of your choice or use in the base of bakes. If you like, garnish with fresh herbs and parmesan.