Place the chicken pieces into a bowl with the soy sauce, ½ teaspoon black pepper, and ½ teaspoon salt. Toss to distribute. Cover and refrigerate for at least 30 minutes. Remove the chicken from the marinade and pat dry with paper towels.
In a gallon size freezer bag, add ¼ cup flour and 1 tablespoon cornstarch. Place the chicken into the bag, seal the bag, and toss until the chicken is completely coated. Place ice into a large bowl. Set aside.
Whisk together the remaining flour, remaining cornstarch, garlic powder, and paprika. Set aside. In a small bowl (that will fit into the larger bowl,) whisk the egg. To the egg, add the flour mixture and mix together until crumbly and well blended.
Add the ice water to the flour mixture and whisk until evenly moistened. Some small lumps are okay. In a large stock pot or dutch oven, heat the oil to 360 degrees or until a drop of batter fries immediately but not too hot that it burns quickly.
Dip the chicken into the batter, allow excess to drip off when lifted, and place into the hot oil. Cook for 3 to 5 minutes per side (depending on the size of your pieces) until the batter is golden and the chicken is cooked through.
Transfer the chicken to paper towels to drain. Serve with sweet and sour sauce, if desired