Preheat the oven to 400°F.

Mix the melted butter, minced garlic, lemon zest, fresh thyme, salt, and black pepper in a small bowl.

Arrange the celery and carrot pieces in a cast iron skillet.

Place the chicken, breast side up, onto the veggies.

Rub the butter mixture generously under the skin of the chicken and inside the cavity.

Stuff the chicken cavity with the head of garlic, onion halves, lemon, and fresh thyme sprigs.

Drizzle olive oil over the chicken skin and brush to coat thoroughly.

Season the chicken liberally with salt and freshly cracked black pepper.

Roast the chicken on the middle rack for 1 hour and 15-30 minutes.

Rest the chicken in the skillet for 10-15 minutes after pulling it from the oven.

Carve the chicken and serve it warm.