Step 1: Prepare the Dipping Sauce : Combine soy sauce, dashi (or water), mirin, sugar, and grated ginger in a small saucepan. Heat gently until sugar dissolves. Remove from heat and let cool slightly.
Step 2: Prepare the Batter : In a bowl, mix flour, cornstarch, and baking powder. Beat egg lightly, then mix with ice-cold sparkling water. Combine wet and dry ingredients gently, leaving lumps—do not overmix to maintain a light, airy batter.
Step 3: Heat Oil for Frying : Heat vegetable oil in a deep pan or wok to 350°F (175°C). Use enough oil to submerge shrimp.
Step 4: Coat and Fry Shrimp : Pat shrimp dry with paper towels. Dip shrimp into batter, then carefully place in hot oil. Fry for 2–3 minutes per side, until golden and crispy. Remove and drain on paper towels. Repeat with vegetables, if using.