Pat the shrimp dry using a paper towel. Place in a bowl, sprinkle turmeric kashmiri chili powder and salt.Marinate for 15-20 minutes.
Add the ingredients listed under coconut paste into a blender jar. Blend to make a smooth paste. Keep ready.
In a shallow pan, warm up 2 tablespoon of oil. Add the shrimp in a single layer. Sear for a minute on each side and remove in a plate. Dont cook the shrimp all the way.
Add another 2 tablespoon of oil to the same pan. Once warm, temper with mustard seeds. Once they crackle, add the fenugreek seeds and dried chilies. Let cook for 30 seconds. Then add the chopped onions and cook for about 5 to 6 minutes until lightly browned.
Next, add the curry leaves along with the kashmiri chili powder. Also add the coconut paste. Saute on low heat for 3-4 minutes until you see the masala glistening.
Add the pureed tomatoes and cook again for 3 minutes or so until you see oil separating on the sides. At this point add the coconut milk and ⅓ to ½ cup warm water. Let the coconut milk simmer for 3 minutes, don't let boil.
Add the seared shrimp to the simmering oconumt milk, add salt and on low medium heat cook for maximum 5-6 minutes until the shrimp are cooked through. If you feel that the sauce is thickish, add ¼ to ⅓ cup additional water.
Finish with tamarind and don't cook a lot after adding tamarind. Take off the stove and garnish with cilantro and serve warm.