Pat the prawns dry using paper towels. Take 1/2 cup of prawns and chop them roughly, then set aside away from the remaining prawns.
Remove the middle vein of the kaffir lime leaves, then roll them up and slice them thinly.
Place the prawns (not the chopped ones), fish, kaffir lime leaves, egg, curry paste, fish sauce, lime juice and sugar in a food processor. Pulse or whizz at low speed until a paste forms.
Transfer the fish and prawn paste into a large bowl. Add in the chopped prawns, spring onions, coriander, and rice flour, then mix well until combined.
Pour enough oil to cover the base of a large frying pan, then heat oil over medium-high heat. Carefully lower 3 or 4 fish and prawn paste into the oil, using a 1/4 cup cookie scoop if available.
Oil a flat spatula and use it to press the paste into flat patties. Cook for two minutes on each side or until golden. Remove the fish cakes from the pan and leave them on a cooling rack with paper towels underneath. Add in more oil if needed, when frying the remaining fish cakes.