Wash and peel 500 grams of potatoes. Cut them into small cubes and soak them in water for 10 minutes. Drain the water and pat the potatoes dry with a clean kitchen towel.
Heat oil in a deep frying pan or kadai over medium heat. Once the oil is hot, carefully add the potato cubes and deep fry them until they turn golden brown and crispy. Remove the fried potatoes from the oil and place them on a paper towel to absorb excess oil.
In a large mixing bowl, add the fried potatoes, 1/4 cup chopped onions, 1/4 cup chopped tomatoes, 1/4 cup chopped coriander leaves, 1/4 cup tamarind chutney, 1/4 cup green chutney, 1/4 cup sweetened yogurt, 1/2 teaspoon chaat masala, 1/2 teaspoon red chili powder, 1/2 teaspoon cumin powder, and salt to taste. Mix well to coat the potatoes evenly with the chutneys and spices.
Transfer the aloo chaat to a serving plate and garnish with a handful of sev and some more chopped coriander leaves. Serve immediately.