Pat chicken thighs completely dry. Season both sides with salt and pepper.
Heat oil in a large skillet over medium-high heat. Place chicken skin-side down. Cook 8 minutes without moving until the skin is deep golden-brown and releases from the pan on its own.
Flip and cook 5 more minutes on the flesh side. Transfer to a plate.
Reduce heat to medium. Pour off all but 1 tbsp of fat. Add garlic and stir constantly for 60 to 90 seconds until fragrant.
Add honey, soy sauce, and apple cider vinegar. Stir and simmer for 2 minutes.
Return chicken to the pan, skin-side up. Add the cornstarch slurry to the sauce around the chicken. Baste every 2 minutes and cook 6 to 8 minutes until the sauce thickens and internal temperature reaches 75°C (165°F).
Remove from heat. Rest 5 minutes. Garnish with spring onions and sesame seeds.