Beef and Molasses Glaze

• 5 kg (11 lb) beef bones with marrow
• 5 brown onions, halved

Preheat the oven to 200°C (400°F). Put the bones in a roasting tin and roast, turning once, until dark brown and caramelised. Transfer to a deep stockpot and cover with water. Add the onions and simmer, covered, over very low