Wash the potatoes and steam or boil with the skin for 15 to 20 minutes. Prick and check if the potatoes are cooked through. Once the baby potatoes are cooked, prick each one of them with a fork all over to make it easy for the potatoes to absorb the spices.
Heat cooking oil at medium to low heat in a kadhai (wok) and add mustard seeds. Once the seeds start to crackle, add cumin seeds and cook till color changes slightly.
Add chopped onion and saute until light brown, followed by ginger & garlic paste. Fry on low heat for 1 minute or till the raw smell disappears.
Now add red chili powder, turmeric powder, amchur powder, salt, and yogurt (you can add a few tablespoons of water if needed). Stir well and cook for a couple of minutes.
Once the masala looks cooked and oil starts to separate, add the pricked baby potatoes and toss well so that it is coated well with all the spices. Place the lid and cook on low flame for 2 minutes. Taste and check the seasoning and adjust accordingly.
Finally, garnish with chopped coriander leaves and sprinkle some chat masala powder.
Serve hot as an appetizer, side dish, starter, or with roti.