Wash the potatoes and boil in water till tender. Take them out and prick them all over with a fork.
Put tomato in a grinder and grind. Transfer the puree to a bowl and keep aside.
Put onion, garlic, ginger and green chilli in a grinder and grind to a paste.
Add about 3 tsp water to yogurt and mix all the spices in it. Stir well to make a paste.
Heat a non-stick frying pan and put oil. When the oil start smoking, add the cummin seeds and stir for a few seconds. Add garlic-ginger paste of step 3 and stir for 2-3 minutes.
Add all the spices of step 4 and cook and cook on medium heat (stir frequently) until oil separates and a mesh type texture results (it takes about 5-7 minutes).
Add tomato puree of step 2 and stir well for 1/2 a minute.
Add potatoes, cover and simmer for 2 minutes.
Garnish with chopped coriander.
Serve with roti, chapatti, naan, bread, etc. or use for burgers.