Peel and cube the potatoes. Mash them slightly and keep aside.
Heat 4 tbsp oil. Add asafoetida and cumin seeds. When they pop, add the mashed potatoes, turmeric, ginger, dry mango powder, sugar and salt.
When they are fried well, add water to make into a thin gravy. When done, remove from heat.
Heat 1 tbsp oil. When it is hot, pour it over the potatoes and immediately sprinkle with chili powder and coriander leaves.
Serve with puris.