Prepare your frying setup by heating vegetable oil in a wok or deep pan to 180°C/356°F, using a deep-fry thermometer to monitor the temperature.
Peel and devein the prawns, keeping their tails intact for easy handling and presentation. Chill them in the fridge until ready to fry.
In a mixing bowl, combine the tempura flour and rice flour (if using). Whisk in the lightly beaten egg and then gently add the ice-cold water, stirring just until the ingredients come together with a lumpy, slightly runny batter. Avoid overmixing to keep it light and airy.
Once the oil reaches the correct temperature, dip each prawn into the batter, allowing any excess to drip off gently.
Carefully lower the battered prawns into the hot oil using a slotted spoon, frying a few at a time to prevent crowding. Listen for a lively sizzle as they hit the oil.
Fry the prawns for about 2–3 minutes, turning occasionally, until the batter is a light golden brown and crispy. The prawns should be opaque and firm when tested with a skewer.
Use a slotted spoon to remove the prawns from the oil, then drain on paper towels to absorb excess oil and keep them crispy.
Arrange the tempura prawns on a serving plate. Serve immediately with lemon wedges or your favorite dipping sauce for maximum crunch and flavor.
