Make the flavored water (pani): in a blender combine the Mint Leaves, Coriander Leaves, Green Chili, Ginger, Tamarind Pulp, Seedless Dates and a little Jaggery for sweetness; add Roasted Cumin Powder, Chaat Masala, Black Salt and Salt with about Water (start with 2 cups) and blitz until smooth.
Strain the blended mixture through a fine sieve into a bowl, taste and adjust seasoning; finish with a squeeze of Lemon Juice and chill the pani for at least 30 minutes so flavors meld.
Prepare the sweet-tamarind chutney: soak and simmer Tamarind with a little water, add more Seedless Dates or Jaggery to sweeten, then blend to a smooth sauce and season with a pinch of Roasted Cumin Powder, Red Chili Powder and Black Salt; cool.
Make the filling: boil and mash the Potatoes and gently crush the Chickpeas; combine with finely chopped Onion and chopped coriander, then season with Roasted Cumin Powder, Chaat Masala, Red Chili Powder, Black Salt and Salt to taste. Mix until well combined but still slightly textured.
Assemble the pani puri: carefully make a small hole in the top of each Puri, spoon in a little potato-chickpea filling and a few chopped onions, add a drizzle of the sweet-tamarind chutney, then immerse the stuffed puri in the chilled pani and pop it into your mouth immediately.
Serve immediately so the puris stay crisp; keep extra pani and chutney on the side for guests to refill as they like.
