Add the olive oil into the frying pan, and then add the chopped onion, crushed garlic and chopped tarragon & mint. Fry until the onion is glazed. (About 3 to 5 minutes)
Then add the tomato puree, stir well for 30 seconds to let caramelize.
Add the vegetable stock & chopped tomato and heat on medium heat for 10 to 15 minutes.
Then remove from heat and use in meals. (see note above)