In a frying pan, add 1/2 teaspoon of ghee, ginger, cumin seeds, green chilly and fry them all till the cumin seeds changes in colour and ginger become little crisp.
Grind the fried ingredients along with salt, coconut and little water. The paste should be super smooth.
Transfer the ground paste into a serving bowl. Add the buttermilk and mix properly. The consistency of tambli should be thinner than chutney, something like rasam consistency. If you want you can add little water along with curd /buttermilk.
Next temper the tambli. In a small kadai, add ghee. When ghee is hot, add mustard seeds and jeera seeds. When mustard seeds splutter, add red chilli / curd chilli and curry leaves.
Add this tempering to the thambli mixture.
Ginger thambli is ready to serve. Enjoy the soothing ginger tambli with rice / drink as such like a coolant ...
Video
Notes
Using fresh coconut and ginger is preferred .
You can also use oil instead of ghee .However ,It is suggested to use ghee because that adds a special aroma characteristic to this dish, so try using it.
The curd / buttermilk you use should be little sour.
Don't add much chilly as ginger would have hotness in it. Also, thamblis are basically mild in nature.
You can skip roasting Ginger in step 1.Else you can directly grind raw ginger along with roasted jeera,g. chilli n coconut. That way you'll have a very strong flavoured ginger thambli. Few prefer that. However, I don't like raw ginger flavour. You can try both n see which way you like.
Always serve the thamblis fresh. It won't taste that great if you refrigerate and use the next day. They just taste OK.