Heat oil in a pan & splutter mustard & fenugreek seeds. Add red chili, small onion, ginger, green chili, curry leaves. Fry it for 1-2 minutes. Add turmeric powder & salt. Mix well.
Add buttermilk and stir. Stir continuously until the steam comes through the spatula. Dont let it boil. It will take around 5-7 minutes. After removing from gas, stir for a few more minutes.
Notes
It can be refrigerated for 3-4 days. It's important that the buttermilk should be at room temperature, otherwise it may curdle. I use low fat buttermilk. If you are using full fat buttermilk, you can add around 1/4 cup water also. I used Al Marai laban to make this