Char the onion and ginger under a hot grill until blackened in spots, then rinse off any burnt bits.

Blanch the beef bones in boiling water for 5 minutes, drain and rinse.

Toast the star anise, cinnamon and cloves in a dry pan for a minute until fragrant.

Combine the bones, charred onion and ginger, toasted spices, fish sauce, sugar and 3 litres of water in a large pot. Simmer very gently, skimming often, for 3 hours.

Strain the broth and season to taste. Poach or thinly slice the beef and cook briefly in the hot broth.

Soak the rice noodles according to the pack, divide into bowls, ladle over the broth and beef, and serve with bean sprouts, basil, lime and chilli.