Step 1

Place 1 boneless, skinless chicken breast inside a gallon zip-top bag. Press out as much air as possible and seal the bag. Using the flat side of a meat mallet or rolling pin, pound the chicken until about 1/2-inch thick. Transfer to a cutting board. Repeat with the remaining chicken breasts.

Step 2

Cut the chicken crosswise into 3/4-inch wide strips (if very large, halve first). Place in a medium bowl. Add 1 tablespoon soy sauce, 2 teaspoons sake, 1/4 teaspoon kosher salt, and 1/4 teaspoon granulated sugar. Peel and finely grate 1 garlic clove and 1 (1/2-inch) piece ginger into the bowl. Toss to coat. Marinate for 1 hour at room temperature or preferably up to 6 hours in the refrigerator.

Step 3

Heat 4 cups neutral oil in a medium pot or wok over medium-high heat until 360°F. Meanwhile, place 1/3 cup all-purpose flour and 1/3 cup potato starch in a medium bowl and whisk to combine. Place 1 large egg in a small bowl and whisk to break up. Add 1/2 cup plus 2 tablespoons cold seltzer or ice water to the bowl with the egg and gently stir. Pour the egg mixture into the flour mixture and stir until just combined. It should look like a thin pancake batter, and lumps are okay. Line a large plate with paper towels, or set a wire rack over a baking sheet and top with a double layer of paper towels.

Step 4

Dip a piece of chicken in the batter until completely coated. Let most of the batter drip off back into the bowl and carefully add to the hot oil. Repeat until about a third of the chicken is in the pot. Fry, turning the chicken occasionally and adjusting the heat as needed to keep the oil at 350ºF, until the chicken is cooked through, 3 to 5 minutes. Transfer to the paper towels or rack.

Step 5

Repeat battering and frying the remaining chicken, using a slotted spoon or spider to skim off the bits of fried batter crumbs in the oil before each batch. Serve immediately.