Prepare the Chicken: Pat the chicken thighs dry with a paper towel. Season them generously on both sides with kosher salt and black pepper. Place the seasoned chicken in a single layer at the bottom of your crockpot.
Mix the Sauce: In a medium bowl, whisk together the bourbon, brown sugar, soy sauce, and minced garlic. Continue whisking until the brown sugar has mostly dissolved into the liquid.
Combine and Cook: Pour the prepared sauce evenly over the chicken in the crockpot. Cover with the lid and set the slow cooker to cook on LOW for 4 hours or on HIGH for 3 hours. For the most tender results, the "low and slow" method is recommended. Avoid lifting the lid during cooking, as this releases heat and can increase the cooking time.
Thicken the Sauce: About 30 minutes before the cooking time is complete, prepare the cornstarch slurry. In a small bowl, whisk the 2 tablespoons of cornstarch and 3 tablespoons of cold water together until a smooth, milky paste forms with no lumps.
Final Simmer: Slowly pour the cornstarch slurry into the crockpot while gently stirring the sauce. This will ensure it thickens evenly. Replace the lid and allow the chicken to cook for the final 30 minutes. The sauce will thicken into a beautiful glaze.
Serve: Once cooked, you can serve the chicken thighs whole or shred them with two forks directly in the crockpot and stir to coat with the sauce. Serve hot over a bed of rice, garnished with freshly sliced green onions for a pop of color and flavor.