Ingredients
4 red onions, 2 roughly chopped, 2 thinly sliced 
1 tbsp vinegar (I used South African brown vinegar) 
1 tbsp lime juice  
2 green chillies, roughly chopped 
400g raw tiger prawns  
4 tbsp oil  
3 large tomatoes, cut into small cubes  
Salt  

Zanzibar Fish Masala Spice 
½ tsp ground cumin
1 tsp ground coriander
½ tsp ground black pepper
¼ tsp ground green cardamom pods
½ tsp ground cinnamon
1 tsp dried lemon grass *  
1 tsp ground ginger  
1 tsp turmeric  
1 tsp paprika  

Buttered rice 
40g butter  
2 tsp cumin seeds  
1 cinnamon stick, broken into 2 
8 green cardamom pods, shelled  
8 cloves  
320g basmati rice  
650ml chicken stock

Method
Take half the masala spice and blend in a processor with the roughly onions, vinegar, lime juice and green chillies until a paste forms.  

Cover the prawns with the paste and leave to marinade for 30 minutes. Wash the rice to remove the cloudy starch and leave soaking. 

In a large frying pan or wok, heat 2 tablespoons of the oil. Add the prawns and all marinade and cook for 3-5 minutes until they just turn pink.  Take the prawns out and put into a bowl. 

Meanwhile while the prawns are cooking, melt the butter and add the spices.  Cook the spices for 30 seconds until fragrant.  Add the washed rice and thoroughly coat with the spiced bitter.  Add the water and bring to the boil.  Reduce the heat to a simmer (a lowish medium heat so it is just barely bubbling), cover with a lid and cook for 10 minutes until cooked (if the rice tastes at all chalky the leave to cook for another minute before testing again). 

While the rice is cooking add the remaining oil on a medium heat and cook the thinly sliced onions until they start to turn golden, this will take 5-7 minutes.  Add the remaining spice mix and cook for another minute stirring.  Add the tomatoes and cook for another 3 minutes.  Add 150ml water, season and simmer until the oil separates at the top of the curry, this will take 5-10 minutes. 

Turn off the rice and cover with a tea towel.  Return the prawns to the sauce and cook for 3 minutes to ensure they are hot all the way through. 

- Taken from The Spice Routes