First, make the dipping sauce. Add the garlic, coriander and chilli in a small mixing bowl mix the in the sugar until dissolved, then add the lime juice and fish sauce. It should taste sweet, salty and spicy.
Combine seasoning mix with the flour. Heat 7/8 cm of oil in a large wok or deep heavy-based saucepan. Dust the prawns with the spice mix, shake off the excess and deep-fry, in batches, for 1-2 mins or until crisp at the edges. Remove with a slotted spoon, drain on a tray lined with kitchen roll and keep warm while the remaining prawns are cooked. Serve with a pot of dipping sauce