Fish Stock — A Spanish Way

• 900g (2lb) fish bits and pieces, including bones and heads
• 1 onion, quartered
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Whack all the ingredients into a very large pan, bring to the boil, cover and simmer for at least half an hour.

If you want a richer, more concentrated stock, reduce the liquid by bubbling it for longer. Strain through muslin or a fine sieve and discard everything apart from the stock itself. Skim and store in the refrigerator for up to 24 hours or freeze for up to 1 month.