In a medium bowl, mix chicken broth, soy sauce, apple juice, cider vinegar, bourbon, ketchup, brown sugar and ground ginger. Reserve.
Place a large skillet or wok over medium-high heat. When hot, add 1 tbsp vegetable oil and half of the cubed chicken in a single layer.
Fry for 2 minutes until lightly browned. Then use kitchen tongs to flip the pieces and cook 2 more minutes on the other side. Remove to a plate.
Wipe the pan clean with paper towel. Add the remaining 1 tbsp oil and fry the remaining chicken pieces the same way. Then remove to the plate.
Add the garlic to the pan and cook for 30 seconds until fragrant. Then add the reserved sauce and bring to a boil for 10 minutes.
Add the chicken to the sauce and boil for 2 more minutes. Season with salt and pepper to taste. Mix the cornstarch with 1 tablespoon of water in a cup and pour into the pan.
Let the sauce thicken stirring constantly for up to a minute or two, just until it's thick enough to coat the back of a spoon. Note that the sauce will thicken further off the heat.
Remove to serving plates and garnish with optional green onions and red pepper flakes.