Put the shallot, garlic, chillies and coriander leaves in a food processor and whizz to a coarse paste. Add the shredded lime leaves and the fish sauce and mix to loosen. Tip into a bowl and season with salt.
Whizz the fish to a rough paste and add to the spice paste, mixing well. Shape into 8 flat round patties with the help of a little flour to stop them sticking to your hands. Set aside for 30 minutes.
To make the dipping sauce heat the vinegar and sugar in a small saucepan until the sugar has dissolved and the mixture is becoming syrupy. Stir in the soy sauce and leave to cool, then add the chillies, coriander leaves and lime juice.
Heat the oil in a shallow pan and when hot fry the cakes ( in batches if necessary) for 4-5 minutes on each side until golden.