Wash and soak the channa dal in sufficient water for 2 hours.
In the meanwhile, clean and prepare the banana flowers. First separate the florets or buds from the banana flower.
For cleaning the banana florets, it is important to remove the inedible stamen from the florets. An easy way to spot this is by gently rubbing the tip of the floret on your palm and the stamen which has a small bulb on top is the one to be removed.
Remove the stamen containing the bulb type structure. In some of the florets, there could even be two, make sure to remove them completely.
Similarly clean and prepare all the banana florets.
Now, finely chop the florets.
Transfer the chopped florets immediately into a bowl containing plenty of water and couple of tablespoons of buttermilk. This is to avoid the florets turning black soon after they are chopped. The chopped banana flowers can be left in this water till we grind the batter for the vada.
Once the dal is soaked well, drain the water completely. Reserve around 3 tablespoons of this soaked dal which we will not grind.
In a mixer, add green chillies, dry red chilli, 1 sprig curry leaf, ginger and garlic and grind till the ingredients are fine.
Now add the soaked channa dal, salt to taste, asafoetida and grind to a very coarse paste by just using the pulse mode. Make sure not to add any water or grind it fine. We need a coarse paste which is what yields a crispy vadai.
The ground dal should look like this and do not grind any further.
Transfer the ground vadai batter to a large bowl. Drain the water from the chopped banana flowers and squeeze them further to get rid of any excess water. Add this drained banana flowers, previously reserved channa dal, roughly chopped onion, 1 teaspoon fennel seeds, finely chopped 2 sprigs of curry leaves, chopped coriander to the bowl.
Mix the vadai batter well. The batter should be crumbly, however hold shape when you try to make a ball.
Heat the oil in Kadai. For making the vadai, take a small portion of the batter and roll it tightly to a ball. The excess moisture when you roll it tightly should be enough to keep the vadai in shape.
Place this ball on one of your palm and using the fingers of other hand, flatten the vada in such a way that the corners of the vada are thin and the centre is slightly thick. This gives the vada the perfect texture, crunch and taste.
Drop the vadai in hot oil, and make more and drop them in the oil. Cook on medium flame by turning them occasionally till they are golden brown in colour.
Drain the Vadai from oil and transfer to a tissue paper. Continue the process to make the remaining vadai.
Serve hot with chutney of your choice or just as is.