I didn't have sesame seeds on hand when I made this, so instead I used chopped green onions as a garnish, and it worked quite well for us. It makes a great presentation too, and it's fabulously delicious.
In small saucepan placed over low heat, combine the cornstarch, cold water, sugar, soy sauce, vinegar, garlic, ginger and pepper. Let simmer, stirring frequently, until sauce thickens and bubbles (about 20 minutes, though cooking time can vary.)
While the sauce is cooking, preheat oven to 425°F (220°). Lightly coat 9x13-inch baking dish with non-stick cooking spray; set aside.
Place chicken pieces in prepared baking dish. Brush chicken with the sauce. Turn chicken pieces and brush other side with more sauce.
Bake in preheated oven for 30 minutes or until no longer pink and juices run clear, and baste with extra sauce every 10 minutes during baking time. Turn chicken pieces and bake another 30 minutes, and continue to baste every 10 minutes.
Cut each thigh lengthwise in 1/2- to 3/4-inch slices and serve over cooked white rice, with some of the sauce spooned over each serving. Sprinkle toasted sesame seeds over each serving, if desired.