1Sweat the onions, in a couple tablespoons of water for a minute or so and then add the garlic. Continue sweating the vegetables being careful not to let the garlic burn.
2Add the chopped tomatoes, the tomato paste, vegetable stock and basil leaves and simmer over a low heat for about 20-25 minutes, or until the tomatoes are completely broken down.
3Strain the mixture through a sieve. At this point, you may return the coulis to the pan and reduce it a little if it is too thin. Alternatively, add a little stock or water to thin it out if it is too thick.
4Adjust seasoning. Just before serving, throw in some fresh basil thinly sliced, if desired.