Pour the stock into a large heavy-based saucepan. Add the ginger, garlic, star anise and peppercorns. Roughly chop one of the chillies and add to the stock. Bring to a gentle simmer and allow to gently simmer for 5 minutes.
De-seed and finely chop the remaining two chillies and put into a food processor with the fish, prawns, spring onions, coriander, two tablespoons of the fish sauce and the kaffir lime zest. Blend until mixed together. I use the pulse button so the mixture keeps some texture. Next roll into bite size balls, keep in the fridge until ready to use.
Pour boiling water over the noodles and leaves to stand for 5 minutes then drain and set aside. Drain the stock to remove the herbs and spices, return to the pan with the rest of the fish
Heat a large frying pan, add the oil and then the fish balls. Fry over a medium high heat for 1-2 minutes, until golden brown and almost cooked through. You will to keep them moving all the time to ensure they colour evenly.
Just before serving, add the fish balls to the stock.
Warm 4 deep bowls and divide the noodles between them. Next pour over the soup and chicken balls ensuring you divide them evenly between the bowls. Finally garnish with spring onions, bean sprouts coriander leaves and lime wedges.