Season steak heavily on both sides with salt & pepper. Let sit for 30 mins. Heat oven to 500. Heat a 12in. cast-iron skillet over high heat until it begins to smoke. Add oil & steak. Cook until lightly charred on one side; about 5 mins. Flip steak & transfer skillet to oven. Cook until medium-rare & an instant-read thermometer reads 135; about 10 mins. Transfer steak to platter & let rest for 10 mins.

Pour off pan drippings & return skillet to stove over high heat. Add butter, thyme & lemon halves, cut sides down. Cook until golden brown; about 4 mins. Remove from heat. Slice steak around the bone. Transfer to plates and drizzle with butter from skillet. Serve with lemon from drizzling.