To prepare the chutney, place tamarind in a large heatproof bowl and pour roughly 3 to 3 ½ cups of hot water. Let the water come to room temperature, and squeeze the tamarind pulp with your hands, removing the seeds as you go along. Once you have removed all the seeds, strain the tamarind juice.
Place the tamarind juice, salt, cumin powder, red chilli pepper and 1 cup sugar in a saucepan. Bring to simmer, and let it cook for 45 minutes to 1 hour until you get the desired consistency. Remove from heat and place in airtight jar.
To get started on the chaat, drain canned chickpeas and place in large bowl. Add diced potato, onion, and tomato. Add salt, chaat masala and 4 tablespoon of tamarind chutney. Mix well. Add finely diced cilantro and mix again. Dust with remaining chaat masala.