Mix the dipping sauce ingredients together in a serving bowl and set aside.
Half-fill a deep saucepan with vegetable oil and heat to 180–190°C (350–375°F), or until a cube of bread dropped into the oil browns in 30 seconds. Just before the oil is hot enough, using a hand whisk, quickly beat the flour, cornflour, salt and sparkling water together in a bowl to make a slightly lumpy batter.
Dip one-third of the vegetables into the batter until coated and then drop straight into the hot oil. Fry for 2 minutes until crisp. Remove from the pan with a slotted spoon, drain on kitchen paper and keep warm in a low oven.
Fry the remaining vegetables in 2 more batches. Serve hot with the dipping sauce.