Parboil potatoes with salt and one-fourth teaspoon of turmeric powder. Drain, cool and halve without peeling them. For the chutney grind fresh coriander leaves, mint leaves, green chillies, garlic and ginger along with salt and lemon juice to a fine paste.
Heat a non-stick pan and dry roast cumin seeds till they give a nice aroma. Add halved potatoes, coriander powder, cumin powder, remaining turmeric powder and mix.
Add half a cup of water, cover and cook on low heat till the potatoes are done. Add the chutney, half a cup of water and mix. Adjust salt and simmer for three to four minutes or till the gravy has thickened.
Add yogurt and stir. Cook till it comes to a boil and take off the heat. Sprinkle toasted sesame seeds and serve hot.