Preheat oven to 400 degrees F.

In a small saucepan, whisk together the cornstarch and cold water until smooth and no lumps. Then, whisk in the sugar, soy sauce, vinegar, garlic, and ground black pepper. Bring to a boil over medium heat then reduce it and simmer until thickens.  You will end up with about 1 cup of sauce.

Trim off any pieces of fat from each chicken thigh using kitchen shears. Place chicken pieces in a 9×13 inch baking dish sprayed with non-stick cooking spray. Pour 1/2 half of the sauce over the chicken, brushing each piece so it is coated.

Bake at 400 degrees for 20 minutes. Turn pieces over and drizzle remaining sauce on top.   Bake for an additional 15 to 20 minutes more until inner temperature reaches 165 degrees or juices run clear.