Char the onion and ginger over a naked flame, turning regularly for 10-15 minutes or until blackened all over. Alternatively, roast them under a hot oven grill. Transfer the onion and ginger to a chopping board and scrape off and discard most of the blackened skins, then roughly chop. Set aside.

Place the beef bones in a large stockpot (at least 6-litre capacity). Pour over enough water to generously cover the bones. Bring to the boil and simmer for 4-5 minutes, then drain. Rinse the bones and clean the stockpot.

Place the bones back into the clean stockpot along with the peeled onion, ginger, star anise, cloves, cinnamon stick, spring onion, and 5 litres of water. Bring to a simmer and cook gently for 4 hours, skimming the surface every so often.

At least 30 minutes before you are ready to serve, soak the dried rice noodles in a large bowl of room temperature water. Drain.

Place the steak into the freezer for 20 minutes before you want to slice and serve. Cut the steak against the grain into very thin slices.

Remove the beef bones from the broth. If you can salvage any meat from the bones, keep that for serving. Strain the broth and place it into a clean pot. Add the sugar, fish sauce, and salt. Taste and season with more fish sauce or salt to your taste.

To serve, drop the noodles in boiling water (do this in individual portions), drain, and place straight into serving bowls. Add some sliced raw onion, spring onion, and some of the braised beef, if using. Drape over thin slices of the raw beef.

Heat the broth up so that it is bubbling before ladling it over the raw beef. Serve with hoisin and sriracha sauce, lemon or lime wedges, chilli, Thai basil, bean shoots, and fish sauce to be added at the table to taste.