Whisk ⅔ cup cornstarch, ⅓ cup all-purpose flour, and ½ teaspoon baking powder together in bowl. Whisk in ¾ cup water until smooth, then refrigerate for 30 minutes. Meanwhile, toss 1½ pounds chicken thighs, trimmed and cut into 1‑inch pieces; 1tablespoon soy sauce; and 1 tablespoon Shaoxing wine in second bowl; cover and refrigerate for 30 minutes.

Set wire rack in rimmed baking sheet. Set second wire rack in second sheet and line with triple layer of paper towels. Add 2 quarts peanut oil to large Dutch oven until it measures about 1½ inches deep and heat over medium-high heat to 400 degrees.

Whisk batter to recombine. Add chicken and toss to coat. Using your hands, remove half of chicken from batter and place in single layer on unlined rack. Let rest for 1 minute to allow excess batter to drip off. Working quickly, use spider skimmer or slotted spoon to lower chicken pieces into hot oil. Using tongs or cooking chopsticks, separate pieces so they fry individually. Fry chicken until light golden brown, about 2 minutes. Adjust burner, if necessary, to maintain oil temperature between 375 and 400 degrees. Using spider skimmer, transfer chicken to towel-lined rack. Return oil to 400 degrees and repeat with remaining chicken; transfer to rack.

Return oil to 400 degrees over medium-high heat. Working in 2 batches, fry chicken a second time until deep golden brown and crisp, 2 to 4 minutes; return chicken to rack lined with fresh paper towels.

Whisk ¼ cup Sichuan chili flakes, 1½ teaspoons sugar, ½ teaspoon table salt, and ¼ teaspoon monosodium glutamate, if using, together in small bowl. Measure out ¼ cup frying oil and set aside; discard remaining oil or save for another use.

Heat empty 14-inch flat-bottomed wok over medium-high heat until just beginning to smoke. Reduce heat to medium-low, drizzle reserved oil around perimeter of wok, and heat until just smoking. Add 6 minced garlic cloves, 4 thinly sliced scallions, and 1 (1-inch) piece ginger, peeled and cut into thin matchsticks, and cook, tossing constantly, until fragrant, about 2 minutes. Add 3 cups small dried Sichuan chiles and 2 tablespoons Sichuan peppercorns and cook, tossing constantly, until just toasted, about 1 minute. Add chicken and sprinkle spice mix evenly over top. Cook, tossing constantly, until chicken is well coated, about 1 minute. Off heat, add ½ cup coarsely chopped cilantro and toss gently to incorporate. Sprinkle with 1 teaspoon toasted sesame seeds and serve.