The way I've always done it is cooked it at 500 for 5 minutes a pound,
then turn the oven off and let it sit it the oven for two hours (do
not open the door). If the internal temperature is not 135 degrees C,
turn the oven up to 375 and cook it until it reaches 135, but it's
usually doesn't take an additional 20 minutes to get it to 135. Let
it sit for 15 minutes, then start carving. Before cooking I rub it
down with a little olive oil then Montreal Steak seasoning.