Mix the sauce: Whisk the chicken broth, soy sauce, rice vinegar, hoisin, brown sugar, the 1 1/2 tablespoons of cornstarch, and the sesame oil together in a small bowl until no lumps remain. Set it next to the stove.

Coat the chicken: Toss the chicken pieces with the salt, then add the 3/4 cup of cornstarch and toss until every piece is dusted white and dry to the touch. Shake off the loose powder as you go and let the coated chicken sit 5 minutes.

Heat the oil: Pour the vegetable oil into a large deep skillet or wok to a depth of about 1/2 inch and heat it over medium-high to 350°F. A pinch of cornstarch dropped in should sizzle right away.

Fry in batches: Fry the chicken in 3 batches, 4-5 minutes per batch, turning once, until deep golden and cooked through to an internal temperature of 165°F. Crowding the pan drops the oil temperature and gives you soggy coating, so leave the pieces room. Drain on a wire rack or paper towels and let the oil come back to 350°F between batches.

Cook the aromatics: Pour off all but 1 tablespoon of the oil. Add the ginger, garlic, and red pepper flakes and cook 30 seconds over medium heat, just until fragrant. They burn fast, so keep them moving.

Thicken the sauce: Whisk the sauce again and pour it into the pan. Bring it to a boil and cook 2-3 minutes, stirring, until it turns glossy and thick enough to coat a spoon.

Toss and serve: Add the fried chicken and toss about 1 minute, just long enough to coat every piece. Pull the pan off the heat, scatter the scallions and sesame seeds over the top, and serve immediately over the cooked white rice.