Prawn and Pork Soup with Rice Noodles

Luke Nguyen: There are many variations of this soup — some add quail eggs, fish or squid. One ingredient that cannot be substituted, however, is Asian celery (also known as Chinese celery). Grown wild in Vietnam, Asian celery resembles an elongated bunch of common celery, but can easily be mistaken for flat-leaf (Italian) parsley, as the stalks are slim and leafy. Dark green in colour, Asian celery is aromatic,