Preheat the oven to 450°F (230°C) and position the oven rack in the middle.
Line the bottom of a broiler pan with foil and place the rack on top; set aside.
In a small bowl, mix the butter with ½ teaspoon salt until combined.
Season the undersides of the chicken breasts generously with salt and pepper.
Carefully loosen the skin from the bottom portion of each chicken breast.
Using a small spoon, divide the butter mixture evenly and spread it under the skin over the meat.
Rub about 2 teaspoons of butter on the outside of each breast skin.
Brush the oil on the skin sides of the chicken breasts to encourage browning.
Place the chicken breasts skin-side up on the prepared rack and roast in the oven for about 20-25 minutes, until the skin is golden brown and the internal temperature reaches 165°F (74°C).
Remove from oven and let rest for 5 minutes before serving to keep juices locked in.