Reserve a handful of boiled sweetcorn for garnishing. Using a food processor, blitz the rest of the drained and boiled sweetcorn coarsely.
Heat oil. Add garlic and briefly sauté for a few seconds. Add the onions along with the salt and sauté until the onions are almost mushy and browned.
Add the minced corn, turmeric powder, coriander and cumin powders and sauté until the mixture is almost dry. Now add the minced mutton and sauté for 30 min on a medium flame. Add the tamarind sauce, garam masala powder and black pepper powder now.
Continue sautéing on a high flame, until the mixture is on the drier side, but not completely dry. This will take around 10 min.
You can make this mixture the previous day and refrigerate. Just before the party, warm the mixture. Scoop out a small portion of this using a teaspoon. Either flatten it on a Paapdi (store-bought) or make a quenelle like I did. Sprinkle some chaat masala on each.
For the sauce, heat the sugar-water mixture on a medium flame, until boiling. Add the rest of the ingredients for the sauce (except the pistachios) and simmer, sautéing continuously, until the mixture is thick. Add the pistachios and stir. Switch off the flame.
Use this sauce generously over each Paapdi Chaat quenelle, ensuring that there is atleast one pistachio on each.