1. Preheat the oven to 400°. In a pot, cover the potatoes with water. Add a large pinch of salt and bring to a boil. Cook over moderately high heat until barely tender, about 10 minutes. Drain and peel the potatoes.
2. In a small skillet, toast the coriander and cumin over moderately high heat until fragrant, about 1 minute. Transfer to a spice grinder and let cool, then grind to a powder and stir in the turmeric and cayenne.
3. Spread the potatoes on a large, rimmed baking sheet and toss with the oil and then the spices. Season with salt and bake for 45 minutes, until tender and crisp. Using a fork, lightly crush the potatoes, then sprinkle with the cilantro and serve.