How to Make It
Prepare the Chicken: Preheat oven to 200°F. Pour oil into a large cast-iron skillet, and fit with a candy thermometer. Heat over medium-high until thermometer reaches 375°F.
Toss together chicken, ginger, and salt in a large bowl until evenly coated. Place 1/2 cup of the potato starch in a shallow dish. Working with 1 piece of chicken at a time, place in starch, and toss to coat completely and evenly. Tap off excess, and place on a baking sheet. Repeat with remaining chicken.
When oil is ready, place about 6 pieces of chicken in hot oil; fry until lightly golden, about 2 to 3 minutes. Flip chicken, and fry another 2 to 3 minutes. Transfer to a baking sheet lined with a wire rack. Repeat with remaining chicken.
When all chicken has been fried once, return chicken, in batches, back to oil to fry again, about 2 minutes per side. Place finished chicken on a separate baking sheet lined with a wire rack, and place in preheated oven to keep warm. Repeat with remaining chicken.
Prepare the Sauce: Stir together gochujang, oyster sauce, mirin, ketchup, fish sauce, and garlic in a medium bowl. Toss chicken with desired amount of sauce, and serve immediately. Sprinkle with sesame seeds.