First heat the OIl, when it's get heated add Mustard Seeds then Cumin Seeds, Curry Leaves and immediately put Potatoes.
Now add Turmeric Powder, cover it and Cook it at medium low heat for 2-3 minutes, stir it after every minute so it can be cook perfectly.
Now add 1 tsp of Red Chili Powder, 1/2 tsp of Asafoetida, now add Water and Salt to taste, again cover it and cook it for 2 minutes, when Potatoes cooked 75% then add the Tomatoes again stir this very well.
Cover it and cook it for further 2-3 minutes, now add Coriander and Cumin Seeds Powder, now just Garnish it with Fresh Coriander Leaves.