Steam cook the potatoes for about 8 minutes. I usually pressure cook, but micrawaving or stove top cooking also works. If pressure cooking, boil water in the pan, and put the potatoes without water in a smaller pan and let the pressure build. Once pressure is achieved, reduce the heat, and cook for 8 minutes on a timed cooker. Maybe 2-3 whistles in an Indian pressure cooker. The goal is to get potatoes that are cooked just enough through, but not mushy.
Peel and chop the potatoes into bite sized cubes when cool enough to handle; I leave the peel on if it's organic
Heat oil in a wide, shallow or broad pan
When hot, add the mustard seeds; when they splutter, add the hing, turmeric, curry leaves, chili powder, and coriander powder and give it a mix; don't let the powders burn
Add the cubed potatoes, salt and keep stirring on medium heat until the potatoes are coated with the spices, browned, and starting to crisp up nicely, about 10 minutes
At this point, it's up to you how long you cook them, to desired crispiness
Enjoy with a hot bowl of rasam rice, sambar rice, yogurt rice or rotis.
I find that the less starchy potato varieties work best for this curry. I typically use the red medium potatoes or sometimes the big yellow ones.
I always pressure cook the potatoes whole and then peel/chop when cool; some peel, chop and then cook in water. Either way would work, as long as the potatoes don't get too mushy/overcooked.
The more oil used, the better the curry tastes, but cooking on a high flame improves the texture and helps crisp them up. Just take care not to burn them
Be liberal with the hing and the curry leaves; the flavor is unbeatable