1. Wash the prawns and shell them without removing the tails. Bring the Tom Yum broth to a boil.2. Add lemongrass, galangal and lime leaves.3. Bring back to a boil then add mushrooms, fish sauce, chilli paste and lime juice.4. Add prawns and fresh chillies.5. As soon as prawns turn pink (cooked through) serve garnished with Thai coriander