In a small saucepan, combine all the sauce ingredients. Bring to boil over high heat, then reduce heat to low and stir until sugar is dissolved, about 3 minutes. Remove from heat and let cool completely. Mix in 1/2 cup water.
Place chicken in a sealable plastic bag. Add soy sauce mixture, seal bag and turn to coat chicken. Refrigerate and marinate as long as you can, up to over-night (*try for at least 1 hour, 4-6 hours is better, 8-10 hours is best).
Remove chicken and set aside. Pour marinade mixture into a small saucepan. Bring to a boil over high heat, then reduce heat to low. Mix cornstarch with water and add to saucepan. Stir until mixture begins to thicken. Remove from heat and set aside.
For baking chicken: Preheat oven to 400 F. Arrange chicken on baking sheet. Brush top of chicken lightly with sauce. Add other vegetables etc in a single layer on the baking sheet as well, if desired. Bake in preheated oven, turning once, until chicken is cooked through, about 20-25 minutes (165F. when tested with an instant read thermometer).
For broiling chicken: Preheat a broiler (6-8 minutes per side/6 inches from heat). Very lightly brush chicken pieces on all sides with sauce, and broil or grill about 3 minutes per side. Test chicken for done-ness. It should be 165F. internal temperature with an instant read thermometer.
Allow chicken to rest a few minutes, then slice. Serve drizzled with warm sauce. Garnish with sesame seeds, if desired.