I learned a while ago that shrimp tempura gets way crispier when everything, even the flour, stays cold. Start by patting your shrimp dry with paper towels and keeping them chilled in the fridge.
In a bowl, whisk together the flour, cornstarch, baking powder, and salt until evenly mixed. Then place the bowl in the fridge to keep the dry ingredients cold.
In another bowl, lightly beat the egg and pour in the ice-cold soda water. The fizz helps create that light, bubbly batter.
Gently add the cold flour mix to the liquid. Use chopsticks or a fork to stir a few times. Don't aim for smooth. Lumpy batter gives a better texture when fried.
Heat the oil in a deep pan to about 170°C (340°F). Test by dropping a bit of batter; it should rise slowly and bubble right away.
Lightly dust each shrimp with flour before dipping them in the batter. That way, the coating sticks better.
Fry 3-4 shrimp at a time for about 1½ to 2 minutes until golden and crisp. Avoid overcrowding. It cools the oil and softens the coating.
Remove and place on a wire rack or paper towel to drain. Keep the oil temperature steady between batches.
Serve the shrimp immediately with the dipping sauce. My go-to is a simple mix of soy sauce, mirin, and grated daikon radish.
Enjoy them while hot shrimp tempura loses its crisp fast, so it’s best fresh out of the fryer.