Step 1: Preheat oven to 400°F (200°C). Pat chicken thighs dry with paper towels. Season lightly with salt and pepper.
Step 2: In a medium bowl, whisk together brown sugar, honey, soy sauce, apple cider vinegar, minced garlic, grated ginger, black pepper, and red pepper flakes (if using) to create the sticky glaze.
Step 3: Heat olive oil in a large oven-safe skillet (like cast iron) over medium-high heat. Sear chicken thighs skin-side down for 5-7 minutes until golden brown and crispy. Flip and sear for another 2-3 minutes.
Step 4: Carefully pour the prepared sticky glaze over the chicken in the skillet. Ensure all chicken pieces are coated.
Step 5: Transfer the skillet to the preheated oven. Bake for 30-35 minutes, basting with the pan juices every 10 minutes, until chicken is cooked through (internal temperature reaches 165°F/74°C) and the sauce has thickened and caramelized.
Step 6: If the glaze isn't as thick as desired, remove chicken from skillet and place on a serving platter. Bring the remaining sauce in the skillet to a simmer on the stovetop over medium heat for 2-3 minutes, stirring until it reduces and thickens. Pour thickened sauce over chicken.
Step 7: Garnish with fresh chopped parsley or green onions before serving. Serve hot with your favorite side dishes.