Fish Stock

• 450 g (1 lb) fish trimmings – head, tails, leftover bones, etc
• 1 onion, chopped

Put all the ingredients into a large pan, bring to the boil, then reduce the heat. Cover and simmer very gently for 30 minutes. Cool slightly, then strain through a fine sieve. Cool completely, refrigerate and use within 1 day, or freeze and keep for up to 1 month.