Method:-
Wash and soak split urad and mung dal (lentils) in enough water for at least 5-6 hours.
Drain the excess water and grind the dal into a smooth batter adding little to no water. Ferment the batter for 4-5 hours till the batter doubles its size and turns spongy.
Grind ginger, cumin seeds and green chillies to a smooth paste.
Add the ginger-chilli paste to the batter and whip it for 3-4 minutes till it turns fluffy. (You can even add raisins and chopped cashews at this stage)

In a steamer boil water and put batter in idli mould tray and steam for 10 to 15 minutes until cooked. Check with tooth pick.
Once cooled soaked the vadas in buttermilk for at least one hour the more is soaked its better.

Remove and place in serving tray.
Whisk the curd and add salt and sugar to taste. Pour over the vadas and garnish with fruits, cumin powder, chilli powder, chat masala, dry fruits and tamarind sauce.
I have decorated in two ways one with fruits only the other one with strawberry and nuts.