To make the dipping sauce, combine water, soy sauce, mirin, and sugar in a small saucepan. Bring the mixture to a boil over medium heat, then lower the heat and simmer until the sugar fully dissolves. Set aside to cool.
¾ cup water, 3 tablespoons soy sauce, 2 tablespoons mirin, 2 teaspoons sugar
Heat the oil in a deep pan to 350°F (180°C). Check the temperature with a thermometer for consistent results.
2 cups vegetable oil for frying
In a large mixing bowl, whisk together the flour, cornstarch, and salt. Create a well and add the iced water stirring gently until just combined—the batter should remain lumpy. Fold in the beaten egg whites carefully to maintain the airy texture.
1 cup all-purpose flour, 2 tablespoons cornstarch, 1 pinch salt, 1 cup iced water, 2 large egg whites
Pat the shrimp dry with paper towels. Dip each shrimp into the batter, making sure it’s well-coated. Fry a few shrimp at a time in the hot oil for about 1 ½ minutes, or until golden brown. Use a slotted spoon to transfer them to a plate lined with paper towels to drain any excess oil.
1 pound medium shrimp
Repeat the battering and frying process with the remaining shrimp, working in small batches to maintain the oil temperature. Serve immediately with the dipping sauce.