Marinate the prawns with salt and ½ tsp black pepper powder. Keep aside for 15 odd minutes.
Heat 1.5 tbsp oil, fry the shallots till light brown. Keep aside.
Shallow fry the prawns lightly in the same oil. Keep aside.
Add the remaining oil to the pan. Throw in the black peppercorns, allow to splutter. Add the fried onion paste, ginger paste, turmeric powder and a little salt. Sauté for 5-7 minutes.
Lower the flame, pour in the whipped yogurt while stirring continuously. Continue to cook over a low flame till oil starts to release from the masala.
Throw in the fried shallots, give it a hearty stir, cook for a further 5 minutes. Add a cup of warm water, bring to a gentle simmer.
Gently add the fried prawns and gondhoraj lebu leaves, sprinkle the remaining black pepper powder and sugar. Cover and cook over a medium flame, another 5 odd minutes or so.
Adjust seasonings, add the gondhoraj lebu zest and some more freshly ground black pepper if you like the heat.
Remove from flame, give it a standing time of 10-12 minutes. Serve hot.