Blanch the spare ribs

• Bring a pot of water to a boil and add the pork spare ribs.
• Blanch briefly to remove impurities, then drain and rinse the ribs under cold water.

Simmer the broth

• Return the ribs to the pot with the water and the onion.
• Bring to a boil, then lower the heat and skim off any foam.
• Simmer gently until the ribs are tender.

Add the vegetables

• Add the potatoes and carrots to the pot.
• Simmer until the vegetables are soft and cooked through.

Season the soup

• Stir in the fish sauce, salt, sugar and black pepper.
• Taste and adjust the seasoning.

Serve

• Ladle the soup into bowls.
• Garnish with spring onions and cilantro and serve hot with rice.