Preheat oven to 425˚F, and line a rimmed baking half sheet with parchment paper
Prepare whole chicken by placing it breast side down. Use kitchen shears to cut through the ribs along the spine on both sides. Use a heavy knife to slightly cut into the sternum, then open rib cage, and pop out the breast bone to flatten the chicken. Season inside the chicken with half the salt and pepper.
Flip the chicken over breast side up and set on the prepared rimmed baking half sheet. Use the palm of your hands to push firmly over the breast bone to allow chicken to flatten. Use your thumbs to pull the skin from the meat.
In a small mixing bowl, combine the ingredients for the garlic herb butter until smooth and well incorporated. Spoon the butter mixture under the chicken skin, and spread any remainder over the chicken.
If you’re preparing vegetables with the chicken, place them around the chicken. Drizzle with olive oil and sprinkle the remaining salt and pepper.
Bake uncovered until instant read thermometer reads 160˚F when inserted into thickest part of chicken breast, about 45 minutes. Remove from oven and rest uncovered for 10 minutes before cutting and serving.