This is one recipe which I like very much. Though I keep making alterations (which I have given at the end of this post).

Yogurt - 2 cups

Water - 2 cups

Salt - To taste

Green Chillies - 2 nos

Ginger piece - 1 inch piece

Curry leaves - 1 sprig

Coriander leaves - 1/4 cup

Hing - 1 pinch

Oil - 1/2 tbsp

Mustard seeds - 1/4 tbsp

Ice cubes - 2 to 4 

Cut green chillies and ginger into small pieces. Beat the yogurt and add water, salt, curry leaves, coriander leaves, green chillies, ginger pieces, hing. 

Temper it with mustard seeds.

You can add 1/4 cup grated cucumber or grated carrot or both to the butter milk.

Decorate the glass with mint leaves before serving.