Directions

1. Feel free to reduce the quantities if you don't need this much stock or don’t have a pot large enough. As a general rule, 1kg (2¼ lbs) of bones will yield about 1 litre (1¾ pints) of finished stock. Use around 15% of the bone weight in vegetables.
2. Preheat your oven to 220°C (200°C fan) or 425°F. Place the bones on a tray, rub them lightly with a neutral-flavoured oil, and roast for 1 hour, turning halfway through.
3. Transfer the roasted bones to a large stockpot. Add a few big handfuls of ice and cover the bones with cold water—this should be about 12 litres (21 pints) of water plus the ice. The ice-cold water will help bring fats and impurities to the surface.
4. Pour off any excess fat from the roasting trays and save it for later. Place the trays over heat, add 500ml (17 fl oz) of water, and scrape up the browned bits from the bottom (fond). Pour this liquid into the stockpot and turn the heat to medium-high.
5. Toss the onions, carrots, and celery with a couple of tablespoons of oil and the tomato purée, ensuring everything is evenly coated. Spread them on one of the roasting trays and roast in the oven for 25 minutes. Set the roasted vegetables aside.
6. Simmer the bones for 10 hours in total. For the first hour, skim off any impurities every 10-15 minutes, then check and skim as needed, roughly every 30-45 minutes.
7. After simmering the bones for 8 hours, add the roasted vegetables. After another hour (9 hours in total), add the herbs, garlic, and black pepper. Simmer for a further 30 minutes before turning off the heat and letting the stock sit for 30 minutes.
8. Carefully ladle the stock through a fine sieve, pulling from the top to avoid disturbing the sediment at the bottom.
9. Leave the stock to cool at room temperature for 2-3 hours before refrigerating it to cool completely.