Soak the beans in cold water overnight. In the morning, rinse them well and boil them in plenty of water for 20 minutes. Drain them, put them back in the pot, add lukewarm water until they are covered by 2 fingers, add the finely chopped onion, the carrots cut into rounds, the celery stalks, the finely chopped tomato, the tomato paste, and the olive oil. Boil the bean soup patiently over medium heat with a covered pot and after about half an hour, add a little salt and plenty of pepper. Boil it for another 20 minutes until it thickens well. If you want, drizzle it with lemon juice. Serve it hot, sprinkling it with the coarsely chopped celery leaves and accompany it with toasted bread, various pickles, and black olives.