Place a medium saute pan for which you have a lid on medium heat. Once hot, add in the olive oil, tomato paste, white part of the spring onion and lime leaf. Cook for 2-3 minutes until fragrant and the tomato paste is just starting to catch.
Make sure that the tomato paste doesn't go dark or the soup will turn bitter.
Add in the chilli flakes, stock, tamarind, soy sauce, palm sugar and ⅛ teaspoon of salt. Mix well, cover with the lid and simmer for 10 minutes on medium low heat. Remove the lid and add in the bean sprouts and cook for another minute until softened.
To serve, divide the savoy cabbage between 4 bowls and ladle in the soup. Top with the remaining spring onions and red chillies.
