De-shell the prawns. Remove the thick black thread that is there in the middle of the Prawns back. This is also known as back-bone.
Apply the turmeric powder, chili powder and salt. Leave this for minimum 30 Minutes. If you want to marinate for longer time, then keep the marinated prawns in refrigerator.
For the gravy:
Grind, grated coconut, turmeric powder, tamarind, peppercorns, coriander and red chilies. After grinding the gravy is ready. We will cook prawns in this gravy.
In a kadai, add 1/4 cup water, marinated prawns and chopped drumsticks. Add 2 tablespoon ground gravy to this. Let it cook for 10 minutes.
Pour in the rest of the ground gravy and stir. Add ½ cup water and cook on a medium flame for 2 minutes.
Let it get cooked for another 10 minutes Switch of the gas.
Now in a tadka/seasoning pan, add oil preferably coconut oil. Once the oil gets heated add chopped onion and fry till it gets burnt. After onion gets bit burnt, give a tadka of burnt onion to the gravy and close the lid.
Add salt to taste. Remember that the prawns were marinated with salt. So add only 1/4 teaspoon salt first. Taste and add more salt if needed.
Note: You can boil drumsticks separately and add it to the curry when it is getting simmered.