Place your chicken into a large bowl and pour your buttermilk over the top, make sure the chicken is well coated. Allow to sit for as long as you can. 12 hours in the fridge would be great, but often I just leave mine for 15 minutes and it works really well.
In another bowl, mix together the flour, starch, herbs and spices and put to one side.
Turn on your air-fryer to preheat. I turn mine on to 190C.
Add a couple of tablespoons of the buttermilk to the coating and mix it through, it will just go a little clumpy.
Take each chicken piece, one at a time, out of the buttermilk and cover in the coating. Using your hands, compact the coating against the chicken as much as poss. Transfer onto a plate until the air-fryer is fully preheated.
Open your air-fryer and place your chicken into the basket - make sure they're not touching each other - this means you might to do your chicken in two batches. Generously spray your chicken with oil. Set the timer for 25 minutes and close the lid.
After about 15 minutes, check on your chicken and turn it over so the other side can colour. Spray any light white, floury bits with a little more oil - these won't turn golden otherwise. Close the lid and allow to cook for a further 10 minutes.
Your chicken should now be golden, crispy and cooked through (you can double check with a cooking thermometer (about 75C is a safe internal temperature).
Repeat with the rest of your coated chicken.
Serve up your chicken with your choice of sides and enjoy!