First boil the potatoes, mash them, salt them, and 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 and thicken gradually. Dissolve the jaggery (or sugar) until 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 a plate, serve the rice-bhel mixture, add the potatoes, then the onions, chilies, and then dust the cumin powder over it. Next pour on the sauce and top with the coriander garnish. (Add salt/pepper to taste). Mix the ingredients on the plate and eat.