Urad dal - 1 1/2 cups, soak in water for 2 to 3 hours
Onion - 1, medium, finely chopped
Spinach - 1/3 cup, chopped and packed OR amaranth leaves/thotakura
Fresh coriander leaves - 1/3 cup, chopped and packed
Fresh mint leaves - 1/3, cup, chopped and packed
Curry leaves - 1/4, cup, chopped and packed
Green chilies - 4, finely chopped
Ginger - 1" knob, finely minced
Cumin - 1/2 tsp (optional)
Salt to taste
Oil for deep frying
Drain the water from the soaked urad dal and grind to a coarse paste adding very little water, approx 4-5 tbsps only. You should feel small bits of dal in the batter.
Place the ground urad dal in a large bowl. Add the chopped onions, green chilies, ginger, spinach, coriander, mint and curry leaves. Add salt and beat the mixture with you hand for a minute.
Heat oil for deep frying in a heavy bottomed vessel. Wet your hand in water, take a large ball of the urad dal mixture in your hand and place it on a moistened plastic sheet. Shape into a flat vadai and make a hole in the center.
Carefully place the shaped vadai in the hot oil. Reduce flame to medium high and make one or two more vadai in the same manner and place in the hot oil. Cook on medium high heat on both sides. You can increase flame towards the end of the cooking process and cook the vadai till crisp and golden brown.
A tip I'd like to share regarding the shaping of the vadai. After making a ball of the batter, place this ball batter on the moistened plastic sheet with a throwing action. This will help thin out the batter evenly on the sheet. Now shape it further and make a hole in the center.
Add salt and onions to the batter just before frying the vadai.
Once you grind the urad dal, use it immediately to make vadai. Otherwise refrigerate it till you use it to make vadai.
To test if the oil is hot or not, drop a small ball of batter in the hot oil. If it sizzles and floats up, it means the oil is ready for deep frying.
The batter should not be runny. It should be thick and aerated.