Take idli batter, grease 3 vati's with butter. Drop the batter 3/4 and steam it for 10-12 mins. Remove when cooled down, keep it aside.

Heat oil, add onions, green chillies and grated ginger. Saute till done. Add the spices, mix it. Add the potatoes. Mix well. Remove from flame. Allow it to cool.

Now take the idli's and cut it horizontally so that it is two parts. Apply the mixture and cover with another half.

Take a tawa, apply butter, roast on both sides till light golden brown.