roughly chop the ginger, green chilli and coriander leaves. keep aside.
now in a small chutney blender, blend coriander leaves, ginger and chilli along with 2 tsp of thick curd / yogurt.
blend to a smooth paste.
in a large blender add 2 cups of yogurt / curd and 1½ cup of cold water. blend well.
combine the ground masala with blended yogurt. add some salt and give a pulse. so everything gets mixed well
for tempering, heat oil / ghee in a small pan and add mustard seeds, urad dal, cumin seeds, red chillies and hing. when the seeds crackle pour the tempering over the buttermilk.
squeeze some lemon juice. garnish with coriander and lemon.