In Italy, they often use small or damaged fish, or the bones of particular kinds like scorpion fish, John Dory or gurnards, as these all have a good strong flavour to impart to a stock. These types of fish aren’t always easy to find, so I add the heads and shells of prawns (shrimp) instead. You can use a bought fish stock for this which is a lot easier but doesn’t have the flavour of a homemade one. If you do buy one, bump up the flavour by adding the cinnamon, chilli, wine and tomato purée from the recipe below.