Put most of the Shallot (10) (reserving 2 tablespoons), Fresh Ginger (1 inch), Garlic (5 clove), Black Peppercorns (1 teaspoon), Ground Turmeric (1/2 teaspoon), Chili Powder (1 teaspoon), and Ground Coriander (1 1/2 teaspoon) into a mortar or blender and pound or blend to a coarse paste, without using any water.
In a bowl, mix the spice paste, Green Mango (1), and Salt (1 pinch) with the Prawns (1 pound). Cover and marinate for 2 hours in the refrigerator.
After the two hours, transfer the mixture to a large pan and heat it over low heat. Cover the pan and gently bring it to a simmer, stirring once or twice. The prawns should release their liquid.
Cover and continue to cook them in their own juices (add a few tablespoons of water only if required) on very low heat for 10-12 minutes, until the prawns and the mangoes are cooked and you have a thick sauce. Taste and season with more salt if required. Turn off the heat.
Heat the Coconut Oil (2 tablespoon) in a small pan. Add the Mustard Seeds (1 teaspoon) and when they pop and crackle, add the remaining shallots and Curry Leaf (10). Fry it all until the shallots are golden.
Take off the heat and pour the mixture on the curry. Serve with plain, steamed rice immediately and enjoy!