Soak the paruppu/chana dhal and the red chilies in water for a minimum of 4 hours
Gather all other ingredients
Finely chop the onions, cilantro, mint, ginger, and the green chilies
Drain the soaked dhal completely, and blend with the fennel seeds and the red chilies. Green chilies may be added to be ground if you don't want to bite into them, I usually chop them finely and add to the batter.
Use very little water while making the batter, as a watery batter won't hold together in the oil. It will also soak up more oil while frying.
Add the chopped ingredients - onions, chilies, cilantro, mint, and ginger, and salt to the batter. Test and adjust salt
Heat the oil in a wide kadai/pan
How to test oil readiness: drop a tiny bit of the batter in the oil; if it sizzles and floats to the top immediately, the oil is ready
Take the batter in small scoopfuls, flatten into the shape of a vadai, about 3-4 inches wide.
For beginners: to do this, take a small lime sized quantity of batter, keeping the batter on four fingers, and shaping them with your thumb into a small flat circle
Gently drop the vadai into the hot oil, from the side of the kadai, very carefully
Fry as many vadais as the pan can take comfortably, not crowding them
After a few minutes, gently turn the vadais in the oil to cook the underside
When the bubbles in the oil start to slow down and disappear, the vadais are done
Serve with chutney/ketchup
The trick to excellent vadais - crisp on the outside, slightly soft but completely cooked on the inside, and a beautiful golden red color is a batter with as little water as you can manage. Sprinkle water as needed when blending
The batter should be slightly coarse, a few half crushed pieces of the dhal add texture and crunch to the vadais
Cook on medium to high heat, and adjust as needed. If the heat is too low, the vadais will take a long time to cook and soak up a ton of oil; if the oil is too hot, the outside will cook too quickly and darken, leaving the batter uncooked/undercooked on the inside
This batter can be prepared ahead and refrigerated until ready to use; in that case, add the salt, onions, and the herbs just before frying. Also, when you fry cold batter, it'll bring down the temperature of the oil and it might have to be adjusted up between batches of frying
If the batter has become too watery in spite of your best efforts, add a couple of tablespoons of rice flour to the batter