The day before you want to cook the chicken, remove the wingtips by cutting through the first wing joint with a sharp knife. Season the chicken generously with salt then let it sit for 30 minutes.
Mix 2 tablespoons of Kosher salt into the buttermilk and stir until dissolved.
After 30 minutes, place the chicken into a gallon-sized plastic bag then pour the buttermilk over the chicken. Seal, massage a bit, then place into the fridge for 24 hours.
An hour before you want to cook the chicken, bring out the chicken and let it come to room temperature. Everything cooks more evenly that way.
Preheat the oven to 425 °F (218 °C) and line a rimmed baking sheet with foil. Place a wire rack on top.
Take the chicken out of the bag and wipe off the buttermilk as much as you can. Don't be obsessive about it; just as much as you can.
Place the chicken on top of the wire rack then with butcher's twine, tie the legs together.
Place the baking sheet diagonally on the center rack in the oven then rotate the pan so the legs are pointed towards the rear left back of the oven.
Cook for 20 minutes then reduce oven temperature to 400 °F (204 °C) then rotate the pan so the legs are pointed towards the rear right back of the oven.
Let cook for another 30 minutes (more or less), until cooked through.
Remove chicken from oven and let sit for 10 minutes before carving and serving.