Peel and devein 500 gms prawns if using prawns in their shell. if you are using peeled prawns skip the next five steps and got straight to the steps beginning with chopping the onion.If you haven't peeled prawns before, here's what you do. First grab the prawn with the index finger and thumb of one hand while holding the body of the prawn in the other. Now twist off the head of the prawn. Put it in one of the bowls. Now use your fingers to prise open the prawn shell along its legs - it should come off easily in one piece if the prawns are fresh. Put this also in the bowl with the head. You will see a little black thread sticking out the end of the prawn's flesh where the head was. That is the pawns gut - also called the vein. You can easily pull this out with your fingers. Don't worry of it breaks. There is nothing wrong with having a bit of prawn gut left in the body of the prawn when you cook it.
Your prawns should look like this.
Put the prawn heads and shells in a saucepan with enough water to just cover them.
Add a pinch of salt, one grind of pepper, 1 tsp coriander seeds and 1 tsp fennel seeds to the pan with the prawn shells.
Put this on the stove. Bring it to the boil. Leave it to simmer for 15 minutes.
While the prawn shells are simmering go on to the next steps. If you are using shelled prawns, this is where you start your preparation of the curry.
Roughly chop 50 gms onion into small pieces.
Roughly chop 1 clove garlic into small pieces like the onion.
Peel a 1 inch piece of ginger and chop it into small pieces too.
Put 4 tbsp vegetable oil into a saucepan and put the pan on the stove.
Let the oil heat up for a minute or so then add the 50 gms chopped onion to the oil.
Now add the chopped clove of garlic and chopped 1 inch piece of ginger,
Let these ingredients cook in the oil for a minute or so.
Now add the leaflets stripped of 1 curry leaf sprig. Careful, they might cause the oil to spit so toss them in and stand back..
Add 1 teaspoon of turmeric powder.
Add 2 tsps of unroasted curry powder.
Add the 5 cm stick of cinnamon. Let all of this cook on a low heat, stirring every now and then to stop it burning. Take the saucepan off the stove after 2 or 3 minutes.
By now, the prawn shells that have been boiling should be nice and pink.
Pour off the water from the prawn shells into a bowl.
Put the prawn shells into a blender and blend them till they form a wet paste.
Pour this paste into the water from the prawn shells.
Pour this mixture into a measuring jug through a strainer or sieve.
Add 150 mls of this prawn stock to the saucepan with the cooked spices. If you have less than 150 mls top it up with water.
Add 150 gms of canned tomato pulp or finely cut fresh tomatoes to the saucepan with the stock and spices.
Add 1 or 2 red chillies chopped very very small.
Add 150 ml of thick coconut milk to the saucepan.
Add the shelled prawns (either those you shelled yourself or those you bought already) to the saucepan with all the liquids and spices.
Bring the liquid to a boil on the stove, turn it down to a simmer, and lets the prawns cook for 15 to 20 minutes.
Just before you serve the prawn curry, squeeze half a lime into the curry. You can also decorate the curry with some lime slices or wedges.