In a cooking pan, heat oil over medium-high heat; when oil is hot, reduce the heat low and add Onion seed and one green chilli, stir few seconds to extract the flavour.
Add Potatoes, sprinkle salt and Turmeric powder, increase the heat to high, and stir for a few seconds. This will help maintain the cooking pot’s temperature.
Then reduce the heat to medium, cover the pan partially, and cook for a few minutes.
Add chopped tomato, green chilli, reduce the heat to medium-low, cover with lid again and continue cooking until potatoes get softened. You need to stir a couple of times.
Add water, increase the heat to high and let the mixture come up to a boil.
Reduce the heat to medium-low. Put the lid on and let it simmer for 7-8 minutes or until potatoes are cooked through and the gravy is thickened up.
Add Sugar and coriander leaves. Give a final stir, remove from heat, cover with the lid and give 10 minutes standing time. The gravy becomes thicker when you allow It to rest. So make sure to turn off the heat when the gravy is a bit runnier than your desired consistency.