Pam, we followed a method in Men's Health magazine. This is the data:
2" thick (that's as long as my thumb) steak, brought to room temperature, dried and rubbed with peanut oil. We used to let the steak air-dry in the refrigerator for a day.
cast iron skillet
Turn oven to 450-500 degrees (not broil).
Put skillet (no oil) in hot oven
After 5 minutes, pull skillet out and add steak.
Have stove-top burner on HIGH. Sear for 3-5 minutes.
FLIP steak, return pan + steak to oven for 5-10 minutes.
Remove from oven, remove from pan and rest for a few minutes.
Smear a dab of soft butter on top
Season liberally with salt and pepper.
Using the shorter times, you end up with a 1/4" sear on each side and a medium-rare steak. Longer times will increase the sear and cook the interior further. You have to make those decisions based on how you like your steak.