Wash the toor dal in water and soak in enough water for at least 4 to 5 hours or overnight for best results.
Peel the shallots and chop them finely, keep aside(if you are using regular onions, make sure you are chopping it finely as it will be difficult to mix large pieces of onions with the batter).
Slice the green chilies in thin round slices, keep aside.
After soaking the dal in water for at least 6 to 7 hours or overnight, drain the water used for soaking and lightly rinse the dal again.
Now we keep aside a little dal separately (which we don't grind as we need them as in the recipe). You can keep aside 2 to 3 tablespoons of soaked dal separately in a bowl which we will use later.
In a good quality food processor, grind together the remaining dal, salt, curry leaves together to make a slightly coarse batter. We do not make this a smooth batter, so make sure not to overly grind the batter. The batter is slightly coarse, which is necessary to make the perfect vada with great texture, crispy on the outside and soft on the inside.
Transfer the grind mixture to a large bowl, and add the sliced green chilies, chopped ginger and onions, and also the extra dal that we kept separately after soaking. Mix all ingredients well until well combined to form the batter for parippu vada. Keep the batter closed for about half an hour for best results.
After 30 minutes, you can just add the extra one spoon of oil to the batter and mix well, which will help you with handling the batter better.
Heat oil in a deep fry pan and once the oil is hot enough, take some batter in your hands to make a ball and gently and slightly press the batter in between your palms (you can oil your palms to make it easy for you to handle) to make a small vada which will look slightly curvy. If you try to make it too much flat, it will have a tendency to break apart. You can avoid this by keeping the shape slightly curvy which means it is little heavier in the middle so it won't break.
Transfer the vada gently to the hot oil, without splashing the oil, for deep frying. I usually transfer the vada first to a large spoon (from the hands) and gently transfer the vada to the hot oil by holding the spoon near to the sides of the pan. This helps me to transfer the vada to the oil without splashing the oil, but this is just an idea you can do it your way just make sure you do it gently without splashing the oil.
At a time, you can fry three to four vada or little more depending on the size of your pan. Make sure not to overcrowd the pan as it will become difficult to handle it. You can fry all the vada in multiple batches.
Once you transferred the vada to the hot oil, wait for the vada to turn golden brown in color on the bottom side which will take a minute or so. Keep the heat medium to high, to avoid the vada from breaking apart. If you are making uzhunnu vada and parippu vada using the same oil, I recommend frying the uzhunnu vada first, as there will be some residue left after making the parippu vada.
Once the vada has turned golden brown on one side, gently flip the vada to fry the other side too, until the vada is golden brown in color on both sides.
Transfer the vada using a slotted spoon (to drain the oil) to a serving plate which can handle hot food( I do not recommend using plastic) which is lined with paper towels to absorb the excess the oil or transfer the vada to a flat surface (which can handle heat) lined with aluminium foil.
Similarly fry all the vada in multiple batches if needed, until all the batter is finished.