Remove the wingtips (or be prepared to put tin foil around them when roasting as they can burn quite quickly)
Season the chicken generously with sea salt and let sit for 30 mins
In a bowl, add the 2 cups of buttermilk and 2 tbsps of sea salt and mix together.Place the chicken into a large sealable plastic bag and pour in the buttermilk. Seal the bag, then squish the buttermilk around so it covers the whole chicken.Put on a plate and pop into the fridge for 24 hrs.
Roasting day
Take the chicken out of the fridge an hour before cooking so it comes to room temperature.Preheat the oven to 220C/425F.
Take the chicken out of the bag and scrape off the buttermilk but don't get obsessive about it. Tie its legs together.
Place in a roasting tray and put into the centre of the oven. It's best to have the legs pointing into one corner of the oven as this is usually the hottest area so you won't dry out your breast first.
After approx 20 mins, the chicken will start to brown so reduce the heat to 200C/400F and cook for another 10 mins, then move the roasting tray so the legs face the other corner of the oven.
Cook for another 30 mins or so, until the chicken is brown all over and the juices run clear (or use a meat thermometer to reach 74 C).Once cooked, remove and rest for 10 mins on a platter before serving.