Marinade the chicken in buttermilk overnight.
In a large bowl, add the chicken pieces and top with buttermilk to fully coat.
Place in the fridge covered in cling film to chill overnight.
Mix all herbs and spices together in a large bowl, including baking powder and flour.
Have beaten eggs in another bowl for dunking.
Remove a piece of chicken from buttermilk, coat in flour spice mix, then into egg, then back into spice mix.
Lay coated chicken on a wire rack.
Line the base of an air fryer with baking parchment and make holes for air flow.
Place chicken in the air fryer and cook at 200C / 390F for approx. 14 mins per side.
Turn halfway for a full cook of approx. 28 minutes.
Check that chicken is cooked through and white, not pink, or use a temperature probe to check it is at least 160C.
Cook in batches and keep the rest warm in the oven.