Boil, peel and cut potatoes in cubes. Chop onions and tomatoes finely using a chopper. Mince green chillies and cilantro. Prepare spicy green chutney and sweet tamarind chutney. You can prepare the chutneys a few days before and store them in the refrigerator. Once all this is ready, its time to assemble the bhelpuri. In a large mixing bowl, add puffed rice, onions, tomatoes, green chillies, spicy green chutney, sweet tamarind chutney, potato cubes, cilantro, lime juice, nylon sev, crushed papdi, chaat masala and black salt. Using a wide spoon or a wide spatula, mix thoroughly until all ingredients are combined fully. The next step is kind of pivotal – taste testing! Adjust the ingredients according to your palate - how spicy, sour, sweet you want your bhelpuri to be, make it so! Garnish with generous amounts of sev and coriander leaves before serving. To keep its authenticity, serve it in paper plates/bowls with a papdi on the side. To get the maximum out of this dish, always make it fresh."