Use a pestle and mortar or a small blender to pound or blend the lemon grass, chillies, garlic, chopped shallots and coriander roots and stalks to form a rough paste. Prepare the prawns (see
Heat 7 cm (3 inches) of oil in a wok over a medium heat. It is ready when a slice of shallot sizzles immediately when dropped in. Deep-fry the sliced shallots for 6–8 minutes until golden brown. Drain on kitchen paper.
Deep-fry the prawns in batches for 3–4 minutes, then drain on kitchen paper.
Remove most of the oil, leaving 1½ tablespoons in the wok. Stir-fry the lemon grass and chilli paste over a medium heat for 3–4 minutes or until fragrant. Add the sugar or honey, fish sauce and tamarind purée or lime juice and cook for 3–4 minutes or until the sugar has dissolved. Add all the prawns and gently toss with the sauce. Taste and adjust the seasoning.
Spoon on to warm serving plates and garnish with coriander leaves and chilli slices.