In a mixing bowl, add buttermilk, coriander leaves, green chile, ginger, salt, and black salt, tempering, and mix well. Taste test and adjust. (If you do not like to chew the coriander leaves or crushed ginger, blend everything with buttermilk in a mixie jar or blender to make this chaas drink.)
2 to 3 cups Buttermilk, 1 tablespoon Coriander leaves, 1 Green chilie, ½ inch Ginger, ¼ teaspoon Salt, ¼ teaspoon Black salt