Pressure-cook 2 medium unripe green mangoes in 2 cups of water over medium heat for 2 whistles, about 8-10 minutes. Let the pressure release on its own.
Strain, keeping the cooking water. Once cool, scrape the pulp from the peels and stones into a bowl.
Add 1½ cups of sugar (about twice the volume of the pulp), 1 teaspoon of ground cardamom, 1 teaspoon of ground roasted cumin, 2 teaspoons of black salt, and ¼ teaspoon of crushed black pepper. Stir until the sugar dissolves.
For each glass, stir 2-3 tablespoons of the mango concentrate into chilled water or some of the cooking water.
