Soak the dal in water for about 2 hours. Drain the water completely. Add the dal, chillies and curry leaves in a mixer. Grind until it is smooth. Check below notes for how to grind the vada batter.
Meanwhile heat the oil in a Kadai.
Wipe the plastic sheet with water. Take a heaped spoon and drop it in the sheet. With wet hands (fingers should be slightly wet and not dripping with water) shape it and make a hole in the centre.
Ulundu Vadai | Urad Dal Vada | Medhu Vada https://www.themagicsaucepan.com/appetizers-snacks/paniyaram-vadai/ulundu-vadai-urad-dal-vada-medhu-vada