The Easiest Thanksgiving Turkey

kosher salt

13-15 pound turkey, spatchcocked/butterflied

onions, roughly chopped

carrots, roughly chopped

stalks of celery, roughly chopped

dried rosemary or 6 sprigs fresh rosemary

vegetable oil

backbone, neck and giblets from the turkey, roughly chopped

onion, roughly chopped

carrot, roughly chopped

stalk celery, roughly chopped

garlic, roughly chopped

homemade or store-bought chicken or turkey stock

bay leaves

unsalted butter

all-purpose flour