Ingredients:
Vada
3 russet potatoes
2 tablespoonsvegetable oil, plus more for frying
1 teaspoonbrown mustard seeds
1 teaspooncumin seeds
1 (1-inch) piece fresh ginger, peeled with a spoon and finely chopped
2 garlic cloves, finely chopped
4 fresh curry leaves
1 teaspoonground turmeric
1/2 teaspoonhing (asafetida)
1/2 teaspoonKashmiri or other red chili powder
Kosher salt
1/2 cuplightly packed finely chopped cilantro leaves
2 teaspoonschaat masala
Fresh lime juice
1 cupchickpea flour (besan)
1 teaspoonground coriander
Chaat
1 tablespoonunsalted butter
4 flaky white buns, such as potato or brioche buns
Green chutney and coconut chutney, for serving
Pan-fried serrano chiles, for serving (optional)
Directions:
Make the Vada: In a medium saucepan, cover the potatoes with water by 3 inches. Bring to a boil over high heat, reduce the heat to medium, and simmer for about 15 minutes, until tender. Drain. Once the potatoes are cool enough to handle, peel with your hands (the skin should slip right off). Transfer the potatoes to a bowl and mash with a fork until mashed but still slightly chunky.
In a medium skillet over medium-high heat, warm 2 tablespoons of the oil until it glistens. Add the mustard seeds and cumin seeds and cook, stirring, for about 2 minutes, until they begin to hiss. Add the ginger, garlic, curry leaves, turmeric, hing, and chili powder. Cook, stirring often, for about 4 minutes, until the garlic is tender. Remove the pan from the heat. Season with salt, then transfer to a large bowl.
Add the potatoes, cilantro, and chaat masala to the bowl with the spice mixture. Stir with a wooden spoon until incorporated. Season with lime juice and salt to taste. Form the mixture into 4 (2-inch) balls and arrange on a plate in a single layer. Cover with a damp cloth; set aside at room temperature.
In a large bowl, whisk the chickpea flour and enough water (begin with ¼ cup) to form a paste that resembles thick cake batter. It shouldn’t be runny. Stir in the coriander; season with salt.
Line a plate with paper towels. Into a deep, heavy pot, pour the oil to a depth of 5 inches and heat over medium-high until a deep-fry thermometer registers 350°F. Dredge the potato balls in the chickpea batter until well coated, shaking to remove any excess. Using a slotted spoon, gently lower a vada into the oil and fry, turning with the spoon to ensure even cooking, for 4 to 6 minutes, until golden brown on all sides. Transfer to the paper towels to drain; season with salt. Repeat with the remaining vada.
Assemble the Chaat: In a large skillet over medium heat, melt the butter. Split the buns and toast, interior side down, for about 1 minute, until light golden brown Place 1 bun, open and interior sides facing up, on each of 4 plates. Slather both sides of the bun with the green chutney, then spoon the coconut chutney on top. Place a vada on the bottom bun and top with the chiles (if using). Serve with additional chutneys on the side.