Prepare the chicken thighs by cutting into 2 to 3 pieces. They should be about the same size as the bao buns.
For the brine, combine chicken, milk, garlic, ginger, salt and black pepper. Set aside for at least 4 hours or overnight.
For the pickled radish, peel the skin. Then, peel the radish to create thin ribbons. Stack the ribbons then slice into thin strips. Combine water, sugar, white vinegar, and salt. Mix until sugar and salt has fully dissolved. Transfer radish into a mason jar or container. Pour the brine into the jar until the radish is completely submerged. Transfer to the fridge and refrigerate for at least 2 hours.
For the sauce, mix together gochujang, soy sauce, ketchup, rice vinegar, honey, sugar, sesame oil, and grated garlic. Set aside for later.
Pat dry the chicken with a paper towel and allow it to air dry at room temperature for 30 minutes before frying.
For the dredge, combine cornstarch, flour, rice flour, baking powder, salt, garlic powder, onion powder, and cayenne pepper. Whisk together to combine.
For the wet batter, combine 1 cup of the dredge with 2/3 cup cold water. Mix until just combined. The consistency should be like pancake batter.
In a deep pan or pot, geat oil over medium heat to 350F (175C).
Dip the chicken in the dredge, then into the wet batter. Allow the excess batter to drain before carefully placing in the hot oil. Fry for 3 minutes. Be sure to work in batches to avoid overcrowding.
Remove and transfer to a wire rack or plate lined with paper towels. Repeat for the rest of the chicken.
To double fry the chicken, increase the oil temperature to 400F / 205C. Fry for 1 to 2 minutes until golden brown and crispy. Make sure to work in batches to avoid overcrowding.
Brush the sauce onto each chicken piece until fully coated.
To assemble the baos, layer the chicken, pickled radish, scallions, and sesame seeds.
Serve and enjoy!