Gently toss 500g of cleaned, deveined prawns with 1/4 tsp turmeric powder and 1/4 tsp salt in a bowl. Let them sit for 10 minutes at room temperature. This brief rest draws out excess surface moisture and seasons the flesh, preparing the prawns to sear beautifully.
Heat 3 tbsp of mustard oil in a heavy-bottomed pan over medium heat. Watch closely until a faint, wispy white smoke begins to rise from the surface. This tells you the raw, harsh pungency of the mustard oil has burned off, leaving behind a smooth, deeply nutty cooking base.
Carefully slide the marinated prawns into the hot oil. Sear them for only 1 minute per side until they turn light pink and form loose 'C' shapes. Immediately scoop them out with a slotted spoon and transfer them to a plate; this prevents them from overcooking and becoming rubbery.
Lower the heat slightly. Add the bay leaf, crushed green cardamoms, cinnamon stick, and cloves into the remaining aromatic oil. Stir for 30 seconds until you hear them sizzle and smell a warm, sweet, exotic aroma release into the air.
Add 1 tbsp ginger paste, the remaining 1/4 tsp turmeric, cumin powder, and Kashmiri red chili powder mixed with 2 tbsp of water (to prevent burning). Sauté for 2 to 3 minutes, stirring constantly, until the water evaporates and you see tiny droplets of oil separating at the edges of the paste.
Pour in 1 cup of thick coconut milk, 1/2 cup of warm water, 1 tsp sugar, and the remaining 1/4 tsp of salt. Stir gently to combine. Bring the mixture to a slow, gentle simmer. You will see a beautiful, glossy golden layer of spiced oil begin to pool on the surface.
Gently slide the seared prawns and any juices collected on the plate back into the simmering gravy. Add 3 slit green chilies. Simmer on low heat for 3 to 4 minutes. The gravy will thicken slightly, and the prawns will become perfectly tender as they absorb the coconut flavors.
Sprinkle 1/2 tsp garam masala powder and drizzle 1 tsp ghee over the top. Stir gently, turn off the heat, and cover the pan with a tight lid for 2 minutes. This traps the volatile aromatic oils inside, infusing the entire curry before you serve.