First boil the potatoes. Mash them and salt them, add pepper to taste. Add some coriander leaves too.
Roast the cumin and grind it.
Dissolve about 4 tbsp of Tamarind concentrate in 1 cup of hot water, and let it simmer to thicken gradually. Dissolve the jaggery (or sugar) till the sauce becomes tart and slightly sweet. (You may add some salt and ground red paprika, if you want to). The sauce should be of a consistency slightly thinner than maple syrup. Pour into a serving container (like a creamer). Mix the puffed rice and sev/bhel mix in a large bowl.
On your plate, serve yourself the rice-bhel mixture, add the potatoes, then the onions, chillies, dust the cumin powder over it. Then pour the sauce. Top with the coriander garnish. (Add salt/pepper to taste).
Mix the goop in your plate and eat it soon.
Note: This is a concoction that I often bought from street vendors in India. My mouth still waters whenever I think of Bhel. The recipe presented here was taken off the net and I haven''t had a chance to try it yet. I include the note from the contributors:
Warning: this recipe is directed at those who know what Bhelpuri tastes like, quantities mentioned are approximate, proportions are left to the readers, to their taste. Purists will have to go to an Indian grocery shop. Deviationists may use substitutes) The most important thing is to keep the puffed rice-sev mixture crisp by not adding the other ingredients to it until serving, and do so on your plate.