In a small bowl, stir together the soy sauce, apple cider vinegar, bourbon, brown sugar, maple syrup, garlic, ginger, and black pepper.
Arrange the chicken in a shallow baking dish, then pour the mixture over the chicken. Cover the dish tightly, transfer to the refrigerator and marinate for as long as time allows (a few hours or overnight).
Lightly coat a 4-to-6-quart crockpot with cooking spray and arrange the marinated chicken thighs in the bottom of the slow cooker. Pour the marinade over the top, then cover the crockpot.
Cook on LOW for 6-7 hours or on HIGH for 2 1/2 - 3 hours, until tender and cooked through.
Remove the chicken from the crock pot to a serving plate and cover to keep warm. Strain the cooking liquid into a small saucepan and place it on the stove.
In a small bowl, whisk together the cornstarch with 2 tablespoons of water to create a slurry. Heat the saucepan on medium-high, then whisk the slurry into the cooking liquid until evenly combined. Cook, stirring constantly, until the sauce bubbles. Continue cooking and stirring until glossy and thickened, 1-2 minutes. Remove from heat.
Pour the sauce over the chicken, then sprinkle with green onions. Serve warm with rice.
SHORTCUT: You may skip marinating the chicken if you are running short on time (or simply forget to do so). The chicken will still turn out delicious just perhaps slightly less tender and flavorful.
INGREDIENT NOTE: I highly recommend using chicken thighs, not chicken breasts in this recipe, as chicken breasts tend to dry out in the crockpot. If you decide to substitute chicken breasts, watch the cooking time carefully, as you may need less time to avoid overcooking the chicken.
TO STORE: Leftover crock pot bourbon chicken may be stored in the fridge for up to 3 days.
TO FREEZE: Store cooked slow cooker bourbon chicken in an airtight, freezer-safe container for up to 3 months. Defrost overnight in the fridge before warming.