Add rice and both dals into the big bowl, wash and drain it for 2-3 times with water, and then soak it in required water for 5-6 hrs or overnight.
Drain the water from the soaked rice-dal mixture. Now add it into the mixer jar (in 2-3 batches) and blend it into the smooth paste. Add little water while grinding and make a batter, it should be little bit thinner than Idli batter.
Mix yogurt well and cover it and place it near the warm place for 7-8 hrs or overnight till it got fermented.
Mix yogurt well in the batter, then cover it and place it near the warm place for at least 5-6 hrs or overnight till it got fermented.
In steamer pot add 2 cup of water and bring it to boiling. Place the stand for dhokla plate inside the steamer.
Take a plate for dhokla, grease it with few drops of oil and keep aside.
Now add ginger-green chili paste(grind 3-4 green chiles; 1/2 Inch ginger to make a paste) , baking soda or ENO, sugar, salt and 1 tsp oil into the batter, mix it well.
Pour prepared dhokla batter into the greased plate till thin layer. Sprinkle some chili powder and ground black pepper on top.
Place the dhokla batter plate into the steamer over the stand, cover the steamer and steam it for 10-12 mins.
Remove the steamed dhokla plate from the steamer and keep aside, use same method for remaining batter to make more steamed dhokla plates.
Let it cool down little bit then cut it using a sharp knife into the square or diamond shape or as per choice.
Now heat oil into the small pan. Add mustard seeds, cumin seeds, sesame seeds and allow it to crackling, then add hing, curry leaves, green chilies and chopped coriander in it. Switch of the flame and pour the prepared tampering all over the steamed dhokla.
Khatta Dhokla is ready, serve it with green chutney or garlic chutney You can also enjoy this fresh, healthy steamed Khatta Dhokla with a hot cup of tea.