1) Sift plain flour, cornflour and salt over a large mixing bowl. Add 120ml of chilled soda water and mix with chop sticks or fork. Add the rest of the soda water and mix. Be careful not to over mix. The lumps give the tempura batter its unique texture.
2) Over moderately high heat, fill a deep pan or wok with about 8cm of vegetable oil. Add vegetables sparingly to the batter making sure they are covered. Place vegetables one at a time in the oil and fry until batter has turned golden brown about 1 minute. Repeat until all vegetables have been cooked.
Serve with soy sauce for dipping.