Wash green mangoes. Cut flesh away from the pit and chop into chunks small enough for your blender. Peel if you want a smoother sip; leave thin peel on for more fiber.

Add chopped mango to the blender with granulated sugar and fresh mint leaves. Top with plenty of ice cubes. Pulse first if needed, then blend until fluffy, pale green-yellow, and the mixture holds soft peaks when you lift a spoon. Scrape the jar once so nothing hides under the blades.

Taste a small spoonful. Add sugar if it is lip-puckering sour. If too thick to pour, blend in cold water one tablespoon at a time until it moves like thick slush or pourable shake.

Stir kala namak, Kashmiri chili powder, and roasted cumin together in a small bowl. Pour slush into chilled glasses and sprinkle a tiny pinch on each serving right before drinking. Serve immediately.