Preheat the oven to 325°F (165°C). Line a 9x13-inch baking dish with parchment paper and set it aside.

Pat the chicken pieces dry, then season them lightly with salt and black pepper.

Place the cornstarch in a large zip-top bag. Add the chicken pieces, seal the bag, and shake well until every piece is evenly coated.

Crack the eggs into a shallow bowl and whisk until smooth.

Heat the vegetable oil in a large skillet over medium-high heat.

Working in batches if necessary, dip the cornstarch-coated chicken pieces into the beaten eggs. Transfer them directly to the hot skillet.

Sear the chicken briefly, turning as needed, until the exterior is lightly golden. The chicken does not need to be fully cooked at this stage.

Arrange the browned chicken in the prepared baking dish.

In a medium bowl, whisk together the granulated sugar, ketchup, apple cider vinegar, soy sauce, garlic powder, and sea salt until well combined.

Pour the sweet and sour sauce evenly over the chicken, tossing gently so the pieces are well coated.

Bake uncovered for 1 hour, carefully tossing the chicken halfway through the baking time so it becomes evenly coated in the thickening sauce.

Check that the chicken has reached an internal temperature of 165°F (74°C), then remove it from the oven.

Let the chicken rest for a few minutes before serving. Spoon the extra sweet and sour sauce over the top and serve with warm rice.