• 1 kg (2 lb 4 oz) fish bones
• 2 stalks celery, chopped
• 1 carrot, chopped
• 1 onion, chopped
• 1 head garlic, halved widthways
• 2 fresh bay leaves
• 2 sprigs thyme
• 10 black peppercorns

Chop the bones into medium pieces and rinse to remove any blood. Place in a large saucepan, cover with 1.5 litres (52 fl oz) water and bring to the boil. Add the remaining ingredients and bring back to the boil, then reduce the heat to low and simmer for 2½ hours, skimming the scum from the surface regularly. Strain, discarding the solids.

This can be made up to 1 day in advance and stored in an airtight container in the fridge.