In a medium bowl, whisk together cold all-purpose flour and cornstarch until smooth, ensuring there are no lumps for an ultra-light, crisp tempura base.

Gently stir in ice-cold sparkling water and a single egg yolk, mixing just until barely combined to keep the batter airy and delicate.

Pat sweet potato, zucchini, carrot, green beans, and shiitake slices completely dry to help the batter cling and achieve an even, golden crisp.

Dip each vegetable piece into the batter, letting excess drip off, and keeping the coating thin to maintain a light, crispy texture.

Preheat 2–3 inches of neutral oil in a heavy-bottomed pot to 350°F (180°C), watching for a shimmering surface before you begin frying.

Carefully lower battered vegetables into the hot oil in small batches; fry 2–3 minutes or until a golden hue appears, flipping gently halfway.

Transfer cooked tempura to a wire rack or paper towels; let drain for a minute to remove excess oil and stay gloriously crisp.

In a small bowl, combine soy sauce, mirin, and freshly grated ginger, whisking until the sauce glistens and flavors meld into a tangy-sweet dip.

Arrange hot tempura around the sauce, sprinkling sliced scallions on top for color and fresh aroma—then dive into that satisfying crunch.