Cut out the backbone of the chicken using the spatchcock technique, and save the backbone for making bone broth. (See video.)
Flatten chicken breast side up and tuck wings under chicken body.
Scatter potatoes, carrots, and onions around the chicken on the sheet pan.
Drizzle everything with olive oil.
Sprinkle salt and black peppers over chicken, potatoes, onions, and carrots.
Dot everything with butter.
Bake in 425°F oven for 45 minutes until chicken skin is golden brown.
Remove from oven, transfer chicken, potatoes, onions, and carrots to a serving platter, bring to the table, and enjoy!