In a bowl, combine chicken cubes with soy sauce and Chinese cooking wine. Let this marinate in the refrigerator for 20 to 30 minutes to allow the flavors to penetrate the meat. After marinating, drain the chicken completely and discard the liquid for food safety.
While the chicken marinates, prepare your coating by combining egg whites and cornstarch in a separate bowl. Whisk this mixture vigorously until it becomes frothy and well-blended. The frothy texture helps create that light, crispy coating we're after.
Add the drained chicken to the egg white mixture and toss thoroughly to ensure every piece is completely coated. This coating will create the golden, crispy exterior when fried.
Heat oil in your deep, heavy-bottomed pan over medium heat. The oil should be hot enough that a small piece of batter sizzles immediately when dropped in. Carefully add the coated chicken pieces to the oil, stirring gently to prevent them from sticking together.
Deep-fry the chicken for 5 to 6 minutes, turning occasionally, until the pieces are golden brown and crispy. Don't overcrowd the pan as this will lower the oil temperature and result in soggy chicken.
Using a slotted spoon, remove the fried chicken from the oil and place on a wire rack to drain excess oil. This step is crucial for maintaining crispiness.
In a clean pan, heat about 1 tablespoon of oil over medium heat. Add the minced garlic and grated ginger, cooking until they become fragrant and slightly softened, about 1 minute.
While the aromatics cook, combine calamansi juice, soy sauce, Chinese cooking wine, sesame oil, brown sugar, and red chili flakes in a bowl. Mix well to ensure the sugar begins to dissolve.
Pour the sauce mixture into the pan with the garlic and ginger. Stir continuously as the sauce heats up and the sugar completely dissolves, creating a glossy, fragrant base.
In a small bowl, whisk together cornstarch and water until completely smooth with no lumps. This slurry will thicken the sauce to the perfect consistency.
Slowly pour the cornstarch slurry into the bubbling sauce while whisking constantly to prevent lumps from forming. Continue cooking for 1 to 2 minutes until the sauce thickens and coats the back of a spoon.
Add the crispy chicken pieces to the thickened sauce and toss gently but thoroughly to coat every piece. The sauce should cling beautifully to the chicken without being too thick or too thin.
Transfer to a serving platter and garnish with toasted sesame seeds and chopped green onions. Serve immediately while the chicken is still crispy and the sauce is warm.