Prepare oven and skillet: Preheat your oven to 425 F degrees. Spray a large skillet with cooking spray. See recipe notes if you don't have a large enough skillet.
Make compound butter: In a small bowl add the butter, poultry herb blend, garlic, lemon zest, salt and pepper. Whisk or mash with a spatula until well combined.
Spatchcock chicken: Place the chicken breast-side down and the legs towards you. Use a pair of kitchen shears to cut up along each side of the backbone, cutting through the rib bones as you go. Open the chicken out and turn it over then flatten the breastbone with the heel of your hand, by pressing down (see video) so that the meat is all one thickness. Cut the wing tips off as well.
Season chicken: Season the inside of the chicken generously with salt and pepper, then flip it over so that the breast side is up.
Apply compound butter: Run your fingers under the chicken skin (breasts and legs) and rub half of the compound butter under the skin. Spread the rest of the mixture over the top of the bird.
Bake: Place the chicken in the prepared skillet and bake uncovered for 45 minutes or until it registers 165 to 170 F on an instant-read thermometer. The time can vary if using a different size chicken.
Let chicken rest: Let the chicken rest at room temperature for about 15 minutes before carving it and serving.
Make gravy: To make the gravy cook the fat drippings from the skillet in a saucepan over medium heat until bubbling. Stir in the cornstarch and chicken broth or water. Stir constantly using a whisk, bring a boil and boil for 1 more minutes. Taste for seasoning and adjust with salt and pepper as needed.