Combine Ingredients:
In a large stockpot, add the blanched oxtail, beef bones, charred onion, and ginger.
Add 3 pieces of star anise, 1 cinnamon stick, and 4 cloves.
Add Water:
Fill the pot with 4 liters of water, ensuring the ingredients are fully submerged.
Simmer Gently:
Bring the pot to a boil, then reduce the heat to a gentle simmer. Skim off any foam or impurities that rise to the surface.
Season the Broth:
Add 3 tablespoons of fish sauce, and adjust with salt and sugar to taste.
Cover and simmer for 3-4 hours to allow the flavors to develop and the oxtail to become tender.