Soak 1 cup of urad dal in water for 4-5 hours, then drain well.
Grind the dal with ⅓ teaspoon of salt and 3 tablespoons of ice-cold water into a thick batter, adding more ice-cold water about 1½ teaspoons at a time only if needed.
Beat the batter by hand until a small ball of it dropped into a bowl of water floats.
Heat 2in / 5cm of oil in a deep, heavy pan over medium heat until a drop of batter rises to the surface.
With moistened fingers, shape a small portion of batter into a ball, flatten it slightly with your thumb, and make a hole in the center. Slide it gently into the oil.
Fry in batches until golden on both sides, letting the oil reheat between batches.
