To cook the chicken, first preheat your oven to 400º degrees Fahrenheit (200°C).
Next, butterfly each chicken. Press down on each chicken to ensure it lies flat. Using your fingers, loosen the membrane and skin under the breasts, thighs and drumsticks. Be careful not to tear the skin. Place a slice of compound or regular butter under each breast, thigh and drumstick. Spread the butter underneath the skin as you go.
Set the chickens onto a baking tray. Drizzle with a bit of olive oil and rub all over the skin. Season with salt and pepper. If you haven’t brined the chicken, you may want to season a bit more liberally.
Place into the oven for about 20 minutes. Then turn the heat down to 350º degrees Fahrenheit and let cook for another 30 minutes or so. Baste both chickens part way through with the drippings from the bottom of the pan.
To check for doneness, flip over and cut off a thigh. Make an incision in the thickest part of the thigh to peek inside. Transfer to another tray in the event that one chicken needs to go back into the oven. Be sure to check both chickens for doneness as they may be different sizes and cook at different rates.
Once done, make sure to let the chicken rest prior to carving. Transfer to a platter. If desired, drizzle with a reduced dark chicken stock and serve.