Soak the lentil for a minimum 2 hours. I usually just do this the night before.Cover it with plenty of water and leave on the counter, just like you'd soak any pulses.
Vadai Spice Mix
When the lentils have had their soaking time, we'll get to the recipe itself.Peel and quarter the onion and drop it into a food chopper.Chop the chilli up into 2 and do the same. Peel and roughly chop the ginger and drop into the chopper.Pick the curry leaves and add to the chopper. Add the coriander leaves as is into the chopper followed by the cumin seeds.Process everything until you have a fine mix.
Heat the oil in a small frying pan on medium heat and fry the spice paste for 3 minutes. Reduce the heat if it starts to catch.You want to fry it until you get a lovely aroma off it and the mix has lost most of its moisture, as it's going to be added to the vadai batter.Set aside to cool.
Clean the Prawns
Traditionally, the prawns would just be rinsed and dried before being used.But if the idea of all that stuff in the prawns head is gross, let's clean it out and also pull the intestinal vein out while we're at it.All you need to do is to gently pull down the prawn head away from the body, to allow you to rinse it with running water. Clean the cavity out.Then gently pull out the intestinal vein and push the head back in place.Or just lose the head altogether!
Make the Vadai Batter
Drain the soaking lentils and rinse them a couple of times. Tip them into your food processor once again (no need to clean it), along with the salt.Grind the lentil to form a fine paste. Add only 1 tsp of water at a time as you're doing this, to achieve a batter that will hold its shape as you form it into a doughnut-like ring.
When you're happy with the consistency, tip it all out into a large bowl. You should have a smooth batter but with a gritty feel.Remember the spice paste we fried earlier? Add this to our vadai batter. Make sure it's not still hot. Mildly warm is ok. If it's hot, give it a stir and 5 minutes to cool down.Mix everything well with your hand. Take a pinch and taste it for salt. Add more if necessary.If you like, you can place your vadai bowl over another bowl filled with cold water to keep it cool. This helps the batter retain its shape while you're forming it and it also creates crispier vadai. Totally optional.
Frying the Vadai
Heat the oil in a medium wok or deep frying pan on medium heat. You want to ensure that the oil is about 5cm/2 inches deep, to allow you to fry the vadai. If your wok/pan is big, you may need to use more oil.Have a plate lined with 3 layers of kitchen paper ready nearby.
Using damp hands (not overly wet), form a ball with the batter and flatten it a little.
Using your thumb, create a whole in the middle, just Like a doughnut.
Place a prawn at the edge and press down a little. That hole will get smaller, don't worry about it.As mentioned in the article above. You could also place the prawn then create the hole. This is all about what works best for you.
Very carefully (that oil is burning hot), slide or drop the vadai into the hot oil. If it's sticking to the side of your pan, after about 5 seconds, use a spatula and nudge it off the sides and into the middle. By this time, the batter will have hardened enough for you to do that.Cook for about 2 minutes on each side, flipping over once.Worried about burning your hands on having trouble with the shape, see the article above on how to do this using a baking paper or banana leaf.
When done, take it out using a slotted spoon and leave to drain on a plate lined with kitchen paper. Sometimes, I forget to take pictures of a step!Repeat with the rest of the batter. Depending on the size of your pan and how quick and comfortable you are with forming the vadai, you can fry about 2-3 at a time. Not too many as it'll lower the oil temperature. If you find that your vadai is browning too quickly, lower the heat to medium-low.Leave to cool for at least 1 minute before serving. But be careful, it'll still be hot.