Heat the olive oil in a large saucepan and sweat the onions, carrot, celery and leek.
Stir in the borlotti beans and parsley stalks. Then add the stock, cherry tomatoes, thyme and garlic. Bring to the boil, then reduce the heat, cover with a lid and simmer for 50 minutes. Stir in the celery leaves. Serve with crostini and a drizzle of extra virgin olive oil.