Wash rice and chana dal. Soak with buttermilk, sugar, and a little water for 5 to 6 hours.
Grind with ginger and chilies into a medium-thick, pourable batter.
Whisk for 3 to 4 minutes to aerate, then ferment until lightly tangy and risen.
Steam the dhokla
Preheat steamer and grease dhokla plate.
Add salt and oil to batter, then mix in Eno just before steaming.
Pour immediately and steam for about 15 minutes on medium-high heat.
Rest for 5 to 10 minutes, then cut.
Tempering and finish
Heat oil, crackle mustard seeds, then add chilies, curry leaves, and hing.
Add water and sugar, bring to a brief boil.
Pour over cut dhokla and garnish with coriander.
Make chutney
Blend all chutney ingredients with little water until smooth.
Serve with warm dhokla.
Notes
For authentic white dhokla color, skip turmeric.Add Eno only when steamer is ready.Store in an airtight container in the refrigerator for up to 3 days.Reheat by steaming for 2 to 3 minutes for best texture.