Peel and finely chop the onion and garlic, then trim and slice the leek. Chop the potatoes, carrots, celery and courgettes, then pick and roughly chop the parsley leaves.
Heat the olive oil in a large saucepan over a medium heat and sauté the onion, garlic and leek for 5 minutes.
Add the other chopped ingredients, the bay, green beans and chopped tomatoes. Drain and add the beans. Cover with water, season and simmer until the vegetables are tender.
Add the pasta and simmer until cooked, adding water if the soup is too thick.
For the pistou sauce, peel and add the garlic to a pestle and mortar, pick in the basil leaves and add some sea salt. Pound until puréed, then finely grate in the Parmesan and muddle in the extra virgin olive oil to make a paste.