In a medium bowl combine sugar, tamari, rice wine vinegar and chicken broth. Set aside.
In a separate bowl, combine chicken pieces with the egg whites and cornstarch, stir until chicken is coated.
Heat the oil in a large skillet or wok until hot. Fry chicken until golden on both sides about 4-5 minutes depending how big your pieces are. You may need to work in batches. Once the chicken is cooked through remove and drain on paper towels.
Leaving a few tablespoons of oil in the wok reduce the heat to medium and saute the garlic and red pepper flakes for 30 seconds, just until fragrant.
Add the tamari sauce mixture to the skillet and increase the heat to medium high. Simmer 10 minutes. then whisk in the remaining cornstarch. When the sauce has thickened add the chicken and toss to coat.
Whisk the remaining cornstarch into 2 tablespoons of water and add to the skillet. When the sauce has thickened add the chicken and toss to coat.
Garnish with green onions, sesame seeds, and serve over jasmine rice and broccoli if desired.