For the soffritto heat the olive oil in a large saucepan and slowly fry the carrot, onion and celery until soft and dark. This will take a long time. Add the garlic, chard stalks, and half the parsley, and continue to cook, stirring to prevent sticking. Add the tomatoes and cook for 10 minutes or until they have reduced.
Add half the Swiss chard leaves and half the cavolo nero, three-qu