In a small bowl, whisk the listed sauce ingredients until combined and the sugar fully dissolves. Set aside.

Dice the chicken thighs into even 1.5-inch pieces. Don't pat them dry; the natural surface moisture helps the cornstarch stick. Transfer to a large bowl and season evenly with salt.

Add cornstarch to the chicken and toss until evenly coated. If wet spots remain, add 1-2 tablespoons more cornstarch as needed.

Heat the oil in a large, heavy-bottomed pan over medium-high heat to 350°F. Fry the chicken in small batches for 5-7 minutes total, keeping the oil at 325-350°F. Don't move the chicken until the bottom is golden and the crust has set; then flip and fry until the other side is golden and the chicken reaches 165°F. Between batches, return the oil to 350°F and remove browned bits. Transfer to a wire rack to keep the crust crisp.

Remove any remaining oil from the pan. Whisk the sauce again and pour it into the pan. Simmer over medium heat for about 30 seconds, or until thick enough to coat the back of a spoon.

Add the fried chicken and toss just until evenly coated. Remove from the heat immediately and garnish with green onions and sesame seeds.