For the filling, place the boiled chane and boiled potatoes in a bowl. Mash the together with your hand. Place the tamarind pulp in a deep bowl.
Add the salt, black salt, roasted cumin powder and red chilli powder and mix well. Stir in four cups of water. Add ice cubes and stir to mix.
To serve, make a hole in the centre of each puri with your thumb; fill the puri with a little potato-chana mixture. Dip the puri into the tamarind water and serve immediately.