For a good fish stock you must use only white fish. With any luck your fishmonger will give you some sole bones and heads, haddock, hake, etc. Make up the rest with some inexpensive fish such as whiting. Cut off and discard the gills in the heads of the fish as they would give the stock a bitter taste.
Makes 1.75 litres (3 pints) stock
1.35 kg (3 lb) white fish bones and heads
3 tbsp olive oil
1 large onion, quartered
2 carrots, thickly sliced
a handful of fennel tops
2 celery stalks, thickly sliced
2 tomatoes, quartered
6 garlic cloves, unpeeled
a dozen peppercorns
4 sprigs flat-leaf parsley
2 bay leaves
1 tsp sea salt
300 ml (1/2 pint) dry white wine
Rinse the fish. Heat the oil, vegetables and garlic in a stockpot and sauté gently for 7–8 minutes. Add the fish to the pan and sauté for 5 minutes to insaporire – give it flavour. Add 3 litres (5 pints) of cold water, the peppercorns, parsley, bay leaves and salt. Bring to the boil and skim well. Simmer for 15 minutes, then pour in the wine and simmer for a further 15 minutes. Strain through a large sieve lined with a piece of muslin. Cool, then skim again if necessary and blot off any surface fat, using kitchen paper.
Transfer the stock to a clean pan and reduce over a high heat until you have only 1.75 litres (3 pints) left.