Fill a large saucepan halfway with water. Peel the potatoes, cut into 2-inch chunks and place into the pot. Add more water as needed to cover the potatoes, then salt the water generously.

Bring to a boil over medium heat and cook the potatoes until tender, about 15 minutes. Drain the potatoes, then return them to the pot off the heat. While hot, use a fork or potato masher to mash the potatoes until smooth.

Heat 1 tablespoon of oil in a large skillet over medium. Saute the onion, garlic, and ginger until the onion is translucent. Stir in 1 teaspoon of the turmeric, cardamom and coriander, then season with salt and pepper. Let cook for 30 seconds until fragrant, then remove from the heat and let cool.

Whisk together the chickpea flour, remaining ½ teaspoon turmeric, a pinch of salt, and egg in a medium bowl until smooth. Slowly add ½ cup water until a thick batter forms. If the batter is very thick at this point, add the additional ¼ cup by the tablespoon until it reaches the consistency of thick pancake batter.

Line a sheet pan with paper towels. Fill a medium heavy bottom pot, such as a Dutch oven, with 3 inches of oil. Heat the oil over medium until it reaches 365ºF.

While the oil is heating, stir the onion mixture and the cilantro into the potatoes until combined. Taste mixture for salt and pepper and adjust to taste. Shape the potato mixture into about 20 golf ball-sized (1 ½-inch) balls.

When the oil comes to temperature, working with 4 or 5 balls at a time, dunk the balls into the chickpea flour batter, then gently lift one at a time with tongs or a slotted spoon and let some of the batter drip back into the bowl. Carefully transfer to the hot oil. Adjust the heat as needed to maintain the oil temperature.

Fry until the batata vada are golden brown, about 5 minutes per batch, then remove to the prepared sheet pan. Repeat with remaining potatoes and batter. Serve immediately.