First wash the potatoes under running water for a long time. Make sure that there is no dirt on the skins. Do not peel the potatoes. Cut them into small cubes, perhaps 1/2 inch cubes or a little bigger than that.
In a sauce pan, boil the potatoes with turmeric powder, red chilli powder and a little bit of salt with about 4 cups of water. Cover and boil till the potatoes become soft.
While the potatoes are boiling, dry roast the coriander seeds slightly and then using a mortar and pestle, crush them a little bit.
Once the potatoes have become soft, take a skillet and heat mustard oil. Temper with dried red chilli, heeng and the crushed coriander seeds. Once they start to splutter, transfer the spices along with the oil into the sauce pan with the potatoes.
Add split green chilies, little bit of sugar. Check the seasoning and add moe salt if required. Give it one boil. If the curry is too runny, then make a slurry with a couple of tsps of whole wheat flour and add to the gravy which will give it some body.