In a large bowl, whisk together buttermilk, flour, cornstarch, egg, hot sauce, salt and pepper, to taste.
Working one at a time, dip chicken into the buttermilk mixture, then dredge in Panko, pressing to coat.
Heat vegetable oil in a large stockpot or Dutch oven to 350°F. Working in batches, add chicken to the Dutch oven and cook until evenly golden and crispy, about 2-3 minutes. Transfer to a paper towel-lined plate; discard excess oil.
Serve immediately, drizzled with bang bang sauce, garnished with parsley, if desired.
For the bang bang sauce
Whisk together mayonnaise, sweet chili sauce, honey and Frank’s Hot Sauce in a small bowl.
Notes
Cut the chicken into similar-sized pieces. Whether you’re using chicken breasts or thighs, dice the chicken into similar bite-sized pieces (about 1-inch chunks) for even, consistent cooking throughout.
Panko yields a flakier crust. Panko is a Japanese-style breadcrumb made from crustless white bread with much larger flakes than traditional breadcrumbs, yielding a crunchier, crispier texture.
Check the temperature. Use a clip-on deep-fry thermometer to maintain a consistent oil temperature (about 325-375°F). If the oil goes past 375°F, the exterior will burn before the inside of the chicken is cooked, and if the oil is too cool, the chicken will absorb most of the oil, resulting in soggy, greasy chicken.
Cook in batches. Cook the chicken in multiple batches as needed to avoid an overcrowded pan. An overcrowded pan will result in a drop in temperature, yielding soggy chicken instead.
Sauce just before serving. This is crucial to avoiding soggy bang bang chicken. Toss or drizzle the cooked chicken with the bang bang sauce just before serving for maximum crispness.
Prepare for leftovers. Store the chicken and bang bang sauce separately if preparing for leftovers to preserve the crisp texture of the chicken bites.