Make the masala paste first. Dry roast the dry spices on a hot griddle without burning the spices and then grind all the ingredients into a smooth paste, adding water only if required.
Marinate the prawns with salt and a dash of turmeric.
In a large wok heat oil and drop in the curry leaves and green chilies, stir for a minute. Next, add the masala paste and cook till masala paste loses its rawness and turns a nice red.
Rinse out the grinder jar with a little water and pour into the wok with the coconut milk. You can use ready made coconut milk but fresh coconut milk tastes much better. Add a cup or two of water and let it come to a boil.
Add washed kokum and salt and let it cook till it has reduced to a suitable quantity. The curry should be thick, not watery.
Prepare the drumsticks while the curry cooks. Peel off the hard outer bark and then chop each drumstick into 4-5 inch batons.
Boil the batons in salted water till just tender. Drain and add them to the curry.
If you're adding potatoes, cut them into medium sized pieces, fry lightly, and then add to the curry as early as you can.
Add the prawns once the curry is nearly ready. Since prawns overcook easily keep an eye on them.
Serve the curry with lots of hot rice, papads and kachumber (a simple salad of sliced onions, cucumber, tomatoes, finely chopped coriander, green chilies, salt, and a few wedges of lime).