Preheat oven to 500°F with a 12-inch cast iron skillet inside.
Season spatchcocked chicken on both sides with kosher salt and fresh cracked black pepper to taste. Drizzle 2 tbsp of olive oil on the skin side of the bird and coat evenly.
Carefully remove preheated cast iron pan from oven and place it on your stove top. Add in the last 2 tbsp of olive oil into the hot pan. Immediately add in the chicken skin side down making sure chicken is as flat as possible.
Place another slightly smaller foil wrapped cast iron or a foil wrapped heavy brick on top of the chicken and firmly press down to flatten chicken. Now carefully transfer this whole thing back into the 500°F oven (make sure to use two hands as this will be very heavy).
Roast chicken for 30 minutes.
After the 30 mins transfer the pan to the stovetop. Remove the top foil lined cast iron/brick. Flip the chicken skin side up. Check temperature at the deepest part of the thigh; should read 165°F when done.
If chicken still needs more time go ahead and pop it back in the oven for about 5 more minutes. Side Note: If chicken is deep golden brown and crispy at this point just bake chicken with skin side up and no top cast iron/brick. If you would like the skin to get a little more crisp/colored feel free to place chicken skin side down with the extra cast iron/brick on top.
Once your chicken is cooked through, transfer chicken from cast iron to a large cutting board to rest. Pour out and reserve pan drippings. Place cast iron on stove at medium heat.