In a large bowl, whisk together the buttermilk and egg. Add chicken pieces and toss to coat. Let marinate for at least 30 minutes, or overnight in the fridge for best flavor.
In a separate bowl, combine flour, cornstarch, garlic powder, onion powder, smoked paprika, salt, black pepper, and cayenne pepper.
Remove chicken from marinade, letting excess drip off. Dredge each piece in the flour mixture, pressing to coat well. Shake off excess flour.
Preheat your air fryer to 370°F for 3–5 minutes.
Lightly spray the air fryer basket with olive oil spray. Arrange chicken pieces in a single layer, skin side down. Spray tops of chicken generously with oil.
Air fry for 15 minutes, flip, spray again, and air fry another 10–15 minutes, or until chicken is golden, crispy, and cooked through (internal temp 165°F).
Remove and let rest a few minutes before serving.