Prepare the vegetables: Ensure all vegetables are washed, dried, and at room temperature. To prep the onion, insert toothpicks at ¼-inch / 6-mm intervals and slice between them.
Cut the eggplants in half lengthwise, then make three long cuts in each half to create a fan shape. Score a decorative crosshatch pattern on the top of each shiitake mushroom cap.
Cut the carrot into 2-inch / 5-cm lengths. 2.
Heat the oil: Pour at least 2 inches / 5 cm of oil into a heavy-bottomed pot or wok.
Heat over medium-high heat until a deep-fry thermometer registers 350°F / 175°C. 3. Make the batter: Just before you're ready to fry, make the batter.
In a small bowl, briefly stir together the all-purpose flour, potato starch, ice-cold carbonated water, and salt.
Do not overmix; the batter should be thin and lumpy.
Add the ice cubes to the bowl to keep it cold. 4. Dredge and dip: Working in small batches of 3-4 pieces, lightly dredge the vegetables in the extra potato starch, shaking off any excess. Immediately dip them into the cold batter, allowing excess to drip off. The vegetable should be thinly and transparently coated. 5.
Fry the tempura: Carefully slide the battered vegetables into the hot oil, ensuring you don't overcrowd the pot.
Fry for about 2 minutes, or until the batter is light golden and crisp. Eggplant may need to be flipped and fried for an additional 2 minutes. 6.
Drain and skim: Use a slotted spoon to remove the tempura from the oil and let it drain on a wire rack. Between batches, skim out any floating bits of fried batter to keep the oil clean. Monitor and maintain the oil temperature. 7.
Serve immediately: Repeat with the remaining vegetables.
Arrange the finished tempura on a platter and serve immediately with warm dipping sauce, grated daikon, and ginger on the side for the best crispy texture.
Keep your batter ice-cold by using chilled carbonated water and adding a few ice cubes directly to the bowl.
Do not overmix the batter. A few lumps are essential for creating that signature light and lacy tempura texture.