Wash and soak the kadalai paruppu and thuvaram paruppu for couple of hours. Then drain them in a colander and keep aside.
Meanwhile, grind the fennel seeds, ginger, garlic, mint leaves, cilantro, green chilies and red chilies into a paste.
Now add the soaked and drained dals to the mixer and grind it coarsely without adding any water. If the mixer seems to be getting stuck, add couple of teaspoons of water and then grind. Make sure that you grind the batter coarsely and not fine. It is absolutely fine to have few pieces of dals left whole. Also add salt when grinding.
After grinding leave the batter in the refrigerator for at least half an hour. This step helps to not soak up lots of oil when deep frying.
In the meantime, chop the onions finely and add this to the chilled vadai batter. Also add the rice flour and mix everything well.
Heat oil in a kadai. Take a handful of batter in your hand and make a ball out of it.
Now flatten the ball using your palm and then drop this into hot oil.
Fry the vadais on both sides until golden brown and then drain them out on paper towels. Note that these vadais are usually a bit on the darker side.
Serve with steaming hot coffee and enjoy the spiciness with every sip of the coffee.