Boil the potatoes in an instant pot or stovetop pressure cooker until soft.
Peel and quarter the potatoes. Take each quarter in your hand and press until it breaks into uneven chunks.
Heat oil in a wok or karahi and add the mustard, cumin and nigella seeds.
When the seeds splutter (30 seconds), add the powdered spices and ginger and garlic pastes. Saute for a minute. Add a few tablespoons of water if required.
Add the potatoes and mix well.
Add 2 cups water, curry leaves, green chilli, tamarind paste, sugar and salt. Cook uncovered for 10 minutes. Aloo curry is ready to be served with pooris.
Notes
Nigella seeds are also known as onion seeds or kalonji. They are black in colour and have a distinctive smell and taste.
Substitute tamarind paste with mango powder or amchur if you want.
Substitute curry leaves with cilantro if you can't get hold of the former.