Toss the prawns with the lemon juice in a shallow non-metallic dish and leave to marinate while you make the sauce. Heat a heavy-based pan with two tablespoons of the oil and then add the onion. Cook for 2-3 minutes until softened but not coloured, then add the turmeric, cardamom pods and chilli powder. Cook for 1-2 minutes until fragrant, stirring constantly.
Stir the remaining oil into the pan with the cinnamon, garlic and ginger. Cook for another 1-2 minutes until the garlic and ginger have softened and are cooked through.
Reserve a few coriander sprigs for garnish and blend the remainder with the coconut cream in a mini food processor.
Stir into pan with the onion and spice mixture until well combined, then bring to the boil. Reduce the heat and simmer gently for 1-2 minutes, then stir in the marinated prawns and season with salt. Continue to simmer for 1-2 minutes until the prawns are just cooked through and tender, stirring constantly.
Garnish the curry with the reserved coriander sprigs and serve with rice or chapattis.