For the marinade and sauce:
¾ cup low-sodium chicken broth
¾ cup freshly squeezed orange juice
1½ tsp. finely grated orange zest
6 tbsp. white vinegar
¼ cup soy sauce
½ cup brown sugar (dark or light)
3 cloves garlic, minced
1 tbsp. fresh ginger, grated
¼ tsp. cayenne pepper
1½ lbs. boneless chicken thighs or breasts, cut into bite-sized pieces
1 tbsp. plus 2 tsp. cornstarch
2 tbsp. cold water
8 thin strips orange peel (optional)
For the coating and frying:
3 large egg whites
1 cup cornstarch
½ tsp. baking soda
¼ tsp. cayenne pepper
3 cups peanut or canola oil (I like a combination)
To make the marinade and sauce, combine the chicken broth, orange juice, orange zest, vinegar, soy sauce, brown sugar, garlic, ginger and cayenne pepper in a large saucepan; whisk to blend well. Measure out ¾ cup of the mixture and transfer it to a large zipper lock plastic bag. Add the chicken pieces to the bag, pressing out the excess air and sealing well. Refrigerate and let marinate 30-60 minutes, but no longer. Place the saucepan with the remaining mixture on the stove and heat over medium-high heat. Bring to a simmer. In a small bowl, whisk together the cornstarch and water until smooth. Add the mixture to the saucepan with the sauce. Continue simmering until the sauce is thick and translucent, about 1 minute. Remove from the heat and stir in the strips of orange peel, if using.
To prepare the coating, place the egg whites in a pie plate and whisk until frothy. In a second pie plate combine the cornstarch, baking soda and cayenne pepper; whisk to blend. Drain the chicken of the marinade in a colander or large strainer; pat dry with paper towels. Place half of the chicken pieces in the egg whites and turn to coat. Transfer the pieces to the cornstarch mixture and coat thoroughly, shaking off the excess. Transfer to a plate and repeat with the remaining chicken pieces.
To fry the chicken, heat the oil in a 11- or 12-inch round Dutch oven or straight-sided sauté pan until the oil reaches 350˚ F. Carefully place half of the chicken pieces in the oil and fry until golden brown, about 5 minutes, turning the pieces halfway through cooking. Remove from the oil with a skimmer or slotted spoon and transfer to a paper towel-lined plate. Return the oil to 350˚ F and repeat with the remaining chicken pieces.
Reheat the sauce if necessary and toss with the cooked chicken pieces. Serve over rice, if desired.