Prepare the prawns by peeling, deveining, and leaving the tails on; then pat them dry and chill in the fridge for about 10 minutes to keep them firm.
In a small mixing bowl, whisk together the beaten egg and ice-cold water until combined; this mixture should feel icy to the touch and slightly bubbly.
In another bowl, combine the all-purpose flour and rice flour, then slowly fold them into the egg mixture with a gentle spatula or chopsticks, mixing just until the batter is lumpy but combined. Do not overmix to keep it light and airy.
Pour about 2 inches of neutral oil into a deep frying pan or wok and heat over medium-high heat until it reaches 180°C (355°F). Use a thermometer to check the temperature, and listen for a gentle sizzle.
Test the batter by dipping a small spoon or piece into the hot oil; it should sizzle immediately and puff up within seconds, indicating the oil is ready.
Using tongs, dip each prawn into the batter, allowing excess to drip off slightly, then carefully lower it into the hot oil. Fry in small batches to avoid overcrowding, which can lower the oil temperature.
Fry the prawns for about 2-3 minutes, turning gently if needed, until the batter is a light, golden, crackling crust. Keep an eye on the color and texture, ensuring they don’t overbrown.
Once cooked, remove the prawns with tongs and transfer them to a wire rack set over paper towels to drain excess oil. Rest for a couple of minutes to maintain crispness.
Squeeze fresh lemon or lime over the hot tempura just before serving to add brightness and contrast to the crispy coating.
Serve the tempura immediately while still crispy, paired with dipping sauce or simply on its own for a delightful crunch and tender prawn bite.
