Place the chicken in a large bowl and toss it with the cornstarch, salt, and black pepper until every piece is lightly coated. The chicken should look dry and lightly dusted, with no loose piles of cornstarch in the bowl.
Warm a wok or large skillet over medium heat, add 1 tablespoon vegetable oil, and arrange the chicken in a single layer, working in batches if needed. Cook for about 6 to 8 minutes until the pieces are browned and cooked through, then transfer them to a covered plate.
Add the remaining vegetable oil to the skillet over medium heat, then cook the scallions for 30 seconds before stirring in the garlic for 20 seconds. The scallions should smell fresh and fragrant, and the garlic should remain pale rather than deeply browned.
Whisk the chicken broth, soy sauce, bourbon, brown sugar, apple juice, apple cider vinegar, and ground ginger in a bowl until the sugar begins to dissolve. Pour the mixture into the skillet and let it simmer steadily for 3 minutes as it lifts the browned bits from the pan.
Return the chicken and any juices on the plate to the skillet, bring the sauce to a boil, then lower the heat to medium-low. Cook for about 5 to 8 minutes, until the sauce thickens into a glossy coating around the chicken.
Remove the skillet from the heat and finish with toasted sesame seeds and sliced green onions if desired. Serve the chicken over cooked rice while the glaze is warm and clingy.