Authentic Japanese Vegetable Tempura

**1. Prepare the vegetables:** - Peel the sweet potato and cut it into 1/4-inch thick slices. - Slice the eggplant, zucchini, and red bell pepper into 1/4-inch thick pieces. - Trim the woody ends off the asparagus and cut into 2-inch pieces. - Slice the king oyster mushrooms into 1/4-inch thick slices. - Lightly dust all the prepared vegetables with a small amount of all-purpose flour to help the batter adhere.

**2. Prepare the batter:** - In a large bowl, combine the all-purpose flour, cornstarch, and baking powder. - In a separate bowl, lightly beat the egg yolk. - Add the ice water to the egg yolk and mix gently. - Pour the egg mixture into the dry ingredients and stir lightly with chopsticks or a fork. The batter should be lumpy; do not overmix to ensure a crispy texture.

**3. Heat the oil:** - In a deep pot or wok, heat the vegetable oil to 170°C (338°F). To test, drop a small amount of batter into the oil; it should sizzle and float to the surface.

**4. Dip and fry the vegetables:** - Dip each piece of prepared vegetable into the batter, allowing any excess to drip off. - Carefully place the battered vegetables into the hot oil, frying in batches to avoid overcrowding. - Fry until golden brown and crispy, approximately 2-3 minutes per batch. - Remove the tempura with a slotted spoon and drain on paper towels.

**5. Prepare the dipping sauce:** - In a small saucepan, combine the soy sauce, mirin, and dashi. - Heat over medium heat until warmed through, then remove from heat. - Serve the tempura hot with the dipping sauce on the side.