Methods

1. Halve and pit the peaches, discarding the pits. Dice the peached and place in a medium bowl with the serrano pepper, brown sugar, and salt, mix well to coat the fruit in the sugar, cover, and let sit at room temperature for at least 1 hour, up to 4 hours.
2. Transfer the fruit-sugar mixture and any juices that have accumulated to a medium saucepan, add the vinegar, and bring to a boil over high heat. Cover, reduce the heat to medium low, and cook until the fruit is tender and starting to fall apart, 10 to 12 minutes.
3. Place a fine mesh sieve over a medium bowl and strain the fruit mixture, gently pressing on the solids to extract as much liquid as possible. Save the pulp for another use. Stir the chaat masala into the shrub, taste, and add more chaat masala, if necessary. Cool, transfer to a jar or bottle, and keep in the refrigerator for up to 1 month.