Melt the butter in a heavy bottom vessel. Heat the butter in a medium flame. I always do the whole process in medium or maybe medium low flame, to avoid burning and stir every 3 minutes or so.
At one stage the butter will completely melt and boils with a sound. After a few minutes, the sound will be ceasing and be careful at this stage. The ghee starts raising and becomes frothy.
When it starts to raise, dip curry leaves in buttermilk and add it to the ghee. Now switch off the flame and keep stirring to avoid the overflow. Now filter in a clean bottle or vessel.
Serve for rotis and use in your recipes. Don't preserve for months, prepare according to your usage and finish it; because we are not adding any preservatives in the ghee. I used curry leaves for flavour, which I learnt from my mom.