Instructions

1. Make the unroasted curry powder: Preheat the oven to 160°F. To a large, rimmed baking sheet, add the coriander, cumin, cinnamon, fennel, fenugreek, cardamom seeds, mustard seeds, and cloves. Spread the spices in an even layer, then place in the oven and bake, shaking the tray every 20 minutes, until the spices are fragrant and dry but not yet colored, about 1 hour. Set aside to cool completely to room temperature.
2. Transfer the cooled spices to a blender or spice grinder and blend to a fine powder. Pass the mixture through a fine strainer, then grind any remaining large pieces. Transfer to an airtight container and store in the fridge for up to 1 month.  
3. Make the curry: Remove the middle shells from the prawns (jumbo shrimp), leaving the heads and tails attached. Place the shells in a small pot, cover with 2½ cups cool water, set over medium heat, and bring to a gentle simmer; cook until the stock is rich and flavorful, about 15 minutes. Remove from the heat, then, using a slotted spoon or spider skimmer, remove and discard the shells. Keep the stock hot while you make the curry.
4. Remove the vein that runs down the back of each prawn, either by butterflying or by sliding a toothpick underneath the vein and gently pulling it out. In a medium bowl, toss the prawns with the ground turmeric and ½ tsp salt, cover and refrigerate for 30 minutes.
5. To a medium pot over medium heat, add the coconut oil and cook just until melted and shimmering. Add the fenugreek seeds, curry leaves, and cinnamon stick and cook, stirring continuously, until the leaves are glossy and fragrant, about 30 seconds. Add the shallots and garlic, and continue cooking, stirring frequently, until the shallots are softened and translucent 5–7 minutes. Stir in 1 tablespoon plus 1½ teaspoons of the unroasted curry powder, the Kashmiri chile powder, and ground coriander and continue cooking until the raw smell disappears and the spices become very fragrant, about 1 minute. (Drizzle a little bit of water into the pan if the spices begin to stick.) Stir in the tomato and cook, stirring frequently, until it breaks down to a dry pulp, 7–9 minutes. Stir in 1 cup of the reserved prawn shell stock, bring to a boil, cook until the liquid has reduced by half, about 10 minutes. Add the coconut milk, bring the sauce to a very gentle simmer, then stir in the tamarind, sugar, and remaining salt.
6. Just before you plan to serve the curry, add the marinated prawns to the sauce. If the sauce is too thick to coat the prawns, add a little bit more of the hot stock to thin. Simmer the prawns until just cooked through, 6–8 minutes. Stir in the green chile (if desired) for the final minute of cooking, then remove from the heat. Season to taste with more salt or sugar. Transfer to a warm platter to serve.
7. Finish with tempered fat: To a small pot over medium heat, add the coconut oil and cook until melted and shimmering. Add the curry leaves, dried chiles, and garlic and cook, stirring frequently, just until fragrant 30–60 seconds. Sprinkle the leaves, chiles, and garlic over the prawn curry, and drizzle over any remaining coconut oil. Serve immediately.