Marinate the prawns with a pinch of salt and 1/2 teaspoon of ground turmeric. Set aside for 10-15 minutes.
In a large pan or wok, heat the mustard oil over medium heat until it starts to smoke slightly. Add the finely chopped onion and sauté until golden brown.
Add the minced garlic, minced ginger, and slit green chilies. Cook for another 2-3 minutes until fragrant.
Add the chopped tomato and cook until the tomato is soft and the oil starts to separate from the mixture.
Stir in the remaining ground turmeric, ground cumin, ground coriander, ground red chili powder, and ground black pepper. Cook for another minute.
Pour in the coconut milk and bring the mixture to a gentle simmer. Add salt to taste.
Add the marinated prawns to the pan and cook for about 5-7 minutes, or until the prawns are cooked through and opaque. Be careful not to overcook the prawns, as they can become tough.
Transfer the Chingri Malai Curry to a serving dish. Garnish with freshly chopped cilantro.
Enjoy your meal!