Soak fox-tail millet/thinai arisi separately and urad dhal with fenugreek separately for four hour's.
Then grind both separately.
Mix both by adding salt(bring to idli batter consistency).
After eight hour of fermentation pour idli's and steam for 10 minutes.
serve hot with any chutney or sambar.
Notes
Not only sambar and chutney even podi will be great with these idli's.
The process is the same as we do for our regular idli's.
This 3:1 ratio worked out well for me,got soft idli's.