Place the chickpeas in a large saucepan, cover with water and bring to the boil, skimming the surface. Partially cover and simmer for 1 hour. Season and cook for a further 15 minutes until tender. Drain.
Season the cod all over with salt, cover and chill for 1 hour.
Meanwhile, for the broth, put the fish bones and trimmings into a large pot and cover with 4 litres of water. Add