Put the chilli powder, paprika, turmeric, garlic, ginger, coriander, cumin, sugar and measured water into a bowl. Mix well and transfer to a large saucepan. Bring this mixture to the boil, then reduce the heat, cover and simmer gently for 7–8 minutes.
Add the coconut milk, salt and tamarind paste and bring to a simmer.
Stir in the prawns and cook briskly until they turn pink and are just cooked through. Serve hot, accompanied by boiled white rice.