In a large bowl, combine the flour, cornstarch, garlic powder, onion powder, salt, black pepper, and baking powder. Mix well.
In another bowl, pour the buttermilk over the chicken pieces, ensuring they are well-coated. Let them marinate for at least 30 minutes (or up to 2 hours in the refrigerator for extra tenderness).
Heat vegetable oil in a deep fryer or a large pot to 350°F. You’ll need enough oil to submerge the chicken pieces.
Remove the chicken from the buttermilk, allowing excess to drip off. Dredge each piece in the flour mixture, ensuring they are fully coated.
Carefully place the coated chicken in the hot oil, frying in batches to avoid overcrowding. Fry for about 8-10 minutes or until golden brown and cooked through. Use a meat thermometer to ensure the internal temperature reaches 165°F.
While the chicken is frying, prepare the sauce by combining gochujang, honey, soy sauce, rice vinegar, minced garlic, and sesame oil in a small saucepan. Heat over low heat, stirring until well combined and slightly thickened (about 5 minutes).
Once the chicken is done frying, remove it from the oil and place it on a paper towel-lined plate to drain excess oil.
Toss the fried chicken in the sauce until well coated.
Serve the chicken hot, garnished with sesame seeds and chopped green onions.