Mix all sauce ingredients, except the cornstarch-water mixture, in a medium saucepan and boil over high heat. Reduce heat to a simmer, over medium-low, and cook for 10-12 minutes. Mix often.

Whisk in the cornstarch-water slurry and bring to a boil, cooking for 1-2 minutes until the sauce has thickened a bit. Remove from heat and set aside to cool.

Whisk together the cornstarch, flour, baking powder, egg, seltzer water, and 1 tablespoon of oil in a large bowl. Set aside.

Season the chicken cubes with salt and pepper.

Transfer the chicken cubes to the flour-water batter and mix them together so the chicken cubes are fully coated. Set aside.

Prepare a cookie sheet lined with a few layers of paper towel for later.

Heat a 6-qt Dutch oven or large pot with oil, so it comes up at least 1/2” in the pot, over medium-high heat. Use an instant read or candy thermometer to check that the oil is between 350°F and 375°F.

Carefully lower 1 chicken cube at a time, using a slotted spoon, into the hot oil, only adding 1⁄3 of the chicken pieces in this batch. Cook chicken for about 4 minutes in the hot oil, stirring occasionally, and carefully flip over each piece halfway through. Place cooked chicken cubes onto the prepared paper towel-lined baking sheet. Repeat in two more batches, so as not to overcrowd the pot.

Transfer the fried chicken to a large bowl & pour the sauce over it. Toss everything together.

Serve with rice and chopped scallions!