Heat the mustard oil in a wok till smoking point and lessen the heat.This is done so that the raw smell from the mustard oil goes away.
Add the kalonjI or kala jeera ,let it splutter, then add the diced potatoes and keep it on medium flame while stirring.
When the potatoes are little cooked add the diced janhi or ridge gourd, turmeric and salt.
Stir it, cover and cook till the curry is 3/4 th cooked.
Add the posto bata or poppy seed paste to the curry let it cook for 2-3 minutes. The posto can be ground in a mixer grinder with garlic and chilly, the poppy seeds can be soaked in little milk for 15 mins before grinding.
Add the water, stir and let the veggies simmer with the paste till it is semi dry and cooked properly which takes nearly 5-7 mins.