Make sure that your shrimps and prawns are de veined and cleaned properly. Remove the heads and the tails and keep them for making something else. You need just the body for this pickle. Then wash and marinade in salt and turmeric powder for about half hour.
While the shrimps are in the marinade, prepare the basic masala. In a frying pan, dry roast Kashmiri red chilies, cumin, fennel, fenugreek and mustard seeds. Once they start releasing oils and your kitchen is fragrant with different aromas, turn off the heat. Cool them down and grind them into a powder.
Take 3 tbsp of sunflower oil in a pan and heat it. Once the oil is hot, fry the shrimps in the same. Some prefer to make them crispy however, I prefer them to be just lightly fried since it will further cook in the masalas.
Drain the shrimps out and keep on a paper towel.
In the same pan, add the balance 2 tbsp of sunflower oil and when hot, add the chopped green chilies. Add the ginger and garlic paste and saute them in medium heat.
When the raw smell of the garlic goes away, add the dry masalas and sprinkle some water or else the masalas will burn. Stir and lightly cook them. Add red chili powder if you want more heat.
Add the prawns and finally the vinegar, sugar and more salt if required.
Continue cooking for about ten minutes or until all the raw smell of the masalas have gone.
When it is almost done, add the mustard oil and turn off the heat.
Once it has cooled down, pour it into a jar and keep outside in the sun for a day or 2. It always tastes right after a couple of days.
It stays well in the refrigerator for a couple of months. Although I promise, it won't last for more than 2 weeks if you are pickle lovers.