In a small bowl or cup, combine the sauce ingredients as listed above and mix to dissolve the sugar. Set aside.
Place chicken thighs skin-side down on a cutting board. Then with the tip of a sharp knife, make small slits around the bone until you can remove it. Pat dry the chicken thighs on both sides with paper towel to remove excess moisture, especially the skin.
Evenly coat the chicken thighs with cornstarch on both sides, shaking off any excess. Set aside on a large plate lined with parchment paper.
Heat vegetable oil in a large pan on medium heat. Sear the chicken thighs skin-side down until crispy golden brown, about 4-6 minutes. Avoid moving the chicken around so it can form a crust. Flip over and fry on the other side until cooked through and golden brown, about 3-5 minutes. Remove chicken from the pan.
Into the pan, add the sauce and scrape the brown bits on the bottom. Simmer for 2 minutes stirring occasionally until slightly thickened.
Add the chicken skin-side down into the sauce. Then quickly flip it over to coat the other side. Remove off heat. Garnish with sesame seeds and green onions. Serve as whole pieces or let it rest for 5 minutes and slice thighs into strips. Enjoy!