Soak urad dal for at least two hours. Drain. Place dal in a food processor. (Grind in batches if needed). Process to a smooth paste. Add a little water if needed. Transfer batter to a large bowl.

Add rice flour, onions, chilies, ginger, curry leaves, and baking soda. Season with salt. Mix. Cover, and leave to rest for 15 minutes.

Meanwhile, heat oil for deep frying in a large frying pan.

Wet your hands with a little water. Take 2 tablespoon of batter , and shape into a ball. Flatten slightly. Using the index finger of the other hand, make a hole in the middle of the vada.

Slide vada into the hot oil. Depending on the size of the pan, you can fry 4-5 vadas at a time. Remember not to overcrowd the pan. Flip the vadas occasionally, and fry for 3-4 minutes or until they are golden on both sides. Drain onto a paper towel.

Serve warm with coconut chutney or sambar.