Sour soup with mussels (somlor machu kreung)

Instructions

1. Clean mussels, pulling off beards.
2. Use a mortar and pestle to start pounding hard-to-grind ingredients: lemongrass, kaffir lime leaves and galangal. Add turmeric, garlic and shallot, and pound until ingredients are crushed and combined into a paste.
3. Heat oil in a large saucepan. Add spice paste and fry for 3–5 minutes, or until dry. Add tamarind paste and chicken stock.  Reduce heat to low and simmer for 10 minutes.
4. Meanwhile, make rice cakes. Heat a little oil in a frying pan over medium heat. Add garlic and cook for 1 minutes, or until fragrant. Add chives and a pinch of salt. Cook for 1 minute.
5. Combine rice flour, tapioca starch and garlic mixture in a mixing bowl. Add enough water, stirring, to make a paste. Add toasted rice mixture and stir to combine.
6. Roll rice mixture into small balls. Flatten into cakes.
7. Heat remaining oil in a frying pan over medium heat. Cook rice cakes, in batches, for 2 minutes each side, or until golden. Set aside.
8. Add cherry tomatoes and water spinach to chicken stock mixture. Add mussels and cover with a lid. Cook for 3–4 minutes, or until mussels are open. Serve soup with rice cakes.