Place the chicken thighs in a large bowl. Add the cornstarch, salt, and black pepper.
Toss until the chicken is evenly and lightly coated with the seasoned cornstarch.
Heat the vegetable oil in a large skillet over medium-high to high heat.
Add the chicken thighs in a single layer. Cook for approximately 4–5 minutes on the first side, until nicely browned.
Flip the chicken and cook for another 2 minutes.
Add the butter to the skillet and allow it to melt. Stir in the minced garlic.
Reduce the heat to medium and cook the garlic briefly until fragrant, taking care not to let it burn.
In a small bowl, whisk together the honey, chicken stock, rice vinegar, and light soy sauce.
Pour the honey mixture into the skillet around the chicken.
Increase the heat briefly to bring the sauce to a gentle boil, then reduce to a lively simmer.
Cook the Honey Garlic Chicken for another 4–5 minutes, turning the chicken occasionally so it becomes thoroughly coated in the sauce.
Continue cooking until the sauce has reduced into a thick, glossy glaze and the chicken reaches an internal temperature of 165°F (74°C).
Remove from the heat and spoon the sticky honey garlic sauce over the chicken.
Sprinkle with chopped parsley and chili flakes. Serve warm over boiled or steamed rice.