For the Sandwich
Soak urad and moong dals separately for 2 hours (it is better to use half and half – equal quantities of both dals the first time, until you get a feel of it). Grind the soaked dals in the blender, until you obtain a slightly coarse (but almost smooth) paste. Pour into a large bowl. Allow this mixture to ferment for 8 – 12 hours, depending on the room temperature. In summer, 8 hours is sufficient, but on cooler days, it takes longer. You can tell whether it is ready or not by the smell. It should have a slightly sour, fermented smell. Add water so that it is of the consistency of dosa batter (somewhat similar to pancake batter). Add salt to taste.
Pour the batter into a square baking dish to a height of about ¼”. Steam in a steamer, until cooked. A toothpick inserted in the centre of the dhokla should come out clean when cooked. Cool, turn out and cut into bite-sized squares. Spread coriander chutney on a square; arrange sliced tomatoes and cucumbers or even sprouts on top, cover with another square and serve.
Serves 6 – 8