Merlu is a deep-sea fish, similar in appearance to cod, but with a more subtle flavour. It is considered one of the best fish in the whiting family because of its firm, sweet, white meat and medium flake. Here it stars in a traditional soup from the Basque region, paired with asparagus, peas and parsley. This recipe takes only 30 minutes to prepare, cook and serve. Of course, crusty bread is the perfect accompaniment.