Wash and soak rice and urad daal in enough water for 7-8 hours.
Now drain the water and wash rice and daal in fresh water .
Grind rice and daal to make a smooth paste like idli batter.
Add tatri, salt and 2 tsp of oil in it and mix well and let the batter ferment overnight or for 8-9 hours.
In a bowl take 1/4 tsp of soda/eno,1 tsp oil and 2 tsp water and mix well.Add this mixture in the fermented batter and mix gently. Boil some water in a steamer and grease the dhokla plates.When water start boiling pour the batter in 2 greased plates. Arrange these plates in the steamer and cover the steamer with a lid.Steam it for 10 minutes on high heat.
Take out the plates from the steamer and unmould after 2-3 minutes.
Now apply chutney on one dhokla (on the rough side).
Place other dhokla over it(keep the rough side over the chutney)Now gently roll it with the rolling pin,so both the layers will stick properly. Heat oil in a small pan and add the tempering ingredients.When sesame become golden then remove it from the heat and add 2 tsp of water in it.
Pour this tempering over the dhokla sandwich.
Cut dhokla in squares or diamonds pieces.
Garnish with chopped coriander and serve.