Soak the beans overnight in a saucepan of cold water. The next day, drain them, rinse well and return to the pan. Cover with water, bring to the boil and simmer for 1 hour. Skim off any froth that rises to the top during cooking. Drain and set aside.
Then make the pistou. You can make it by hand in a pestle and mortar, or use a small blender. Combine the garlic and basil leaves until they have almost formed a paste. Slowly mix in the olive oil, add the seasoning and place to one side.
To make the soup, heat the olive oil in a saucepan and sauté the onion, celery, leek, potatoes and carrot over a medium-low heat for 20 minutes without browning them. Add the vegetable stock, haricot beans and seasoning, and simmer for 20 minutes.
Meanwhile, score the skin of the tomatoes and plunge them into a pan of boiling water for 10 seconds, then remove and peel away the skin. Cut into quarters, remove the seeds and dice the remaining flesh. Cut the beans into 2.5cm lengths, finely dice the courgette and slice the artichoke hearts into quarters. Add to the simmering soup along with the vermicelli and tomato and cook for 10 more minutes. Serve with a spoonful of the pistou on top of each bowl.