Season the chicken generously and allow to sit for 30 minutes.
Add 1 tbsp Sea Salt to the Buttermilk and pour into a resealable bag. Add the chicken to the bag and make sure the entire chicken is marinated in buttermilk. You may need to double bag. Put into the fridge for 24 hours.
Remove the chicken from the fridge one hour before you want to cook and remove as much of the buttermilk as possible.
Blend together the lemon, cumin, coriander (if using), thyme, garlic, ghee/butter, salt and pepper.
Loosen the skin from the breast and spread the blended butter mixture under the skin of the chicken as far as you can. Season generously, both inside and out.
Tie the legs together.
Place the chicken breast side down, into a narrow 10 inch pot or shallow roasting tin. Try and keep th legs pointed towards the back of the oven.
Place into the oven and leave to cook for 30 minutes basting once every 15 minutes. Turn the chicken onto its back and cook for 30 minutes basting at 15 minutes.
Turn the heat up to 250 C/Gas Mark 9 and cook for a further 15 minutes.
Remove from the oven and rest for 10 minutes before serving.