Pat the chicken thighs dry and place in a bowl; toss with cornstarch, salt, and ground pepper until evenly coated.
In a small bowl, whisk together chicken stock, honey, soy sauce, rice vinegar, red chili flakes, and chopped parsley; set the sauce aside.
Heat a skillet over medium heat and add the oil. When hot, add the chicken thighs and cook 5–6 minutes per side, flipping once, until browned and cooked through.
Push the chicken to the side, add the butter to the center of the skillet, and when melted stir in the minced garlic; cook about 1 minute until fragrant.
Pour the prepared sauce into the skillet, reduce heat to medium-low, and simmer for about 5 minutes until the sauce thickens and coats the chicken.
Remove from heat and serve the honey garlic chicken immediately.