1Whisk together the buttermilk, salt, smoked paprika, onion powder, garlic powder, and black pepper in a large bowl, add the chicken, toss to coat, and let sit.
2Combine the flour, cornstarch, salt, smoked paprika, onion powder, garlic powder, black pepper, ground mustard, and cayenne if using in a large bowl.
3Remove the chicken from the buttermilk, letting excess drip off, then toss well in the seasoned coating, pressing it onto the chicken.
4Dip the chicken briefly back into the buttermilk and coat once more in the flour mixture for an extra-crispy coating.
5Heat 2–3 inches of neutral oil to 350°F and fry the chicken in batches until golden brown and cooked through.
6Transfer chicken to a wire rack and immediately sprinkle with flaky sea salt.
7Combine BBQ sauce, honey, butter, apple cider vinegar, smoked paprika, and black pepper in a small saucepan, heat over medium-low until butter melts, then simmer briefly.
8Add the hot crispy chicken to a bowl, drizzle with the Honey BBQ sauce, and toss gently to coat.