For the pork and prawn balls:
1. Mix all the ingredients together.
2. Oil your hands and roll the mixture into balls.
3. Heat a little oil in a frying pan and lightly fry the balls to give them a little colour set aside.
To make the soup:
1. Heat the chicken stock with Kaffir lime, lemongrass and fish sauce.
2. Add the prawn and pork balls and heat through.
3. Ladle into bowls and garnish with vermicelli, coriander, bean sprouts and chilli and serve.