1 tablespoon panch phoran (available in Indian markets)
½ teaspoon freshly ground black pepper
1 inch fresh ginger, peeled (use the edge of a teaspoon to scrape off the skin) and finely chopped
3 medium stalks rhubarb, ends trimmed and stalk chopped into ½- to 1-inch pieces
¼ teaspoon kosher salt
Directions
In a medium saucepan set over medium-high heat, bring the water, lime juice and sugar to a simmer, stirring occasionally, until the sugar is dissolved. Add the curry leaves, cardamom, chiles, cinnamon, panch phoran and black pepper and cook, stirring often, until the spices become fragrant, 1 to 2 minutes.
Add the ginger and stir until fragrant, about 1 minute, then stir in the rhubarb and salt. Reduce the heat to medium-low, cover and cook, stirring often, until the rhubarb collapses into a sauce, 6 to 8 minutes. Uncover and continue to cook until a wooden spoon leaves a trail in the bottom of the pot that doesn't immediately fill in, 25 to 35 minutes. Turn off the heat and cool to room temperature, then transfer to a serving dish or an airtight container, cover and refrigerate for up to a week.