Preheat the oven to 375 degrees F (190 degrees C).
Pour cornstarch and garlic salt into a large resealable bag.
Dip chicken pieces in beaten egg. Remove and drop chicken into cornstarch mixture and seal the bag.
Shake the chicken in the bag until all pieces are fully coated.
Heat vegetable oil in a skillet over medium heat. Cook and stir chicken in heated oil until browned, about 5 minutes.
Stir vinegar, sugar, chicken broth, ketchup, soy sauce, and salt together in a bowl.
Arrange the browned chicken in a baking dish; pour the vinegar mixture over the chicken.
Bake in preheated oven until chicken is no longer pink in the center and juices run clear, about 40 minutes.