Place the steak into a vacuum sealable bag. Remove as much air as you can, being careful not to suck in any liquid out of the bag.
Set your immersion circulator to 130-135 degrees for medium rare. Or up to 140 for medium. I don't recommend cooking it more than 140.
Place the steak into the water bath. Set a timer for 2 hours.
Remove the steak with a pair of tongs after the 2 hours is up.
Add some oil to a cast iron pan. Set the pan over high heat and wait until the pan is sizzling hot. Then cook the steak for 30-45 seconds per side to just get it browned.