Wash and clean the urad dal 2-3 times and then soak it in sufficient water for 2-3 hours.
Drain the soaked urad dal well and grind it coarsely in a mixer/blender using very little water. I used a quarter cup and a tablespoon of water for grinding.
Finely chop the spinach leaves, curry leaves, coriander leaves and basil leaves or mint leaves. Add this into the ground urad dal batter.
Add finely chopped onions, finely chopped/grated ginger, finely chopped green chillies, black pepper (optional) and salt as per taste into the batter.
Blend and mix the Vadai batter lightly by hand using a spatula or a spoon to make the batter light and fluffy.
Heat sufficient oil in a heavy bottomed deep pan. The oil should neither be too hot not too cold.
If oil is too hot, the vadai will cook quickly with inside not cooked properly. If the oil is cold, the the vadai will become soggy. If you drop a bit of batter into the oil , it should rise to the top and then brown.
Take some water in a bowl. Wet your palm and take some batter in your palm. Pat the batter lightly so as to form a doughnut not more than 1/4 inch thickness and make a hole in the center with your thumb.
When the oil is optimum hot, lower the heat and carefully invert your palm over the oil and drop the keerai vadai slowly into the oil. If you are not comfortable, just drop the batter as doughnut balls into the oil.
Cook each side on low medium heat for 3-4 minutes each or till the side turns light golden color. Crank up the heat slightly and cook each side for 1-2 minutes to make it crispy.
Take out the vadai on a plate and drain out the excess oil using a kitchen paper towel or any absorbent material. Cook in batches of 2-3 keerai vadai and take care to not overcrowd the wok.
Serve the keerai vadai hot and enjoy with coconut chutney, sambhar or any spicy chutney.