Set a dry skillet over medium heat (do not use a nonstick skillet for this). Add the cumin seeds, coriander seeds, and peppercorns and heat, shaking the pan occasionally, until the spices are fragrant and toasted, about 2 minutes.
Allow the spices to cool, then grind them to a powder in a spice mill. Add the ginger, mint leaves, and salt and continue to grind u