1. Place chicken in a shallow dish or large zip-top plastic freezer bag.
2. Process quartered onion, 2 Tbsp. sugar, and next 7 ingredients in a blender or food processor until smooth, stopping to scrape down sides; pour over chicken. Cover or seal, and chill 2 hours.
3. Remove chicken from marinade, discarding marinade. Sprinkle sesame seeds evenly over chicken; place in a lightly greased shallow roasting pan.
4. Bake at 375º for 50 to 55 minutes or until done. Garnish, if desired.