Add the seasoned tenderloin to a vacuum seal bag and use your vacuum sealer to seal. If you don't have a vacuum sealer, use another air removal method.
Set up your immersion circulator in your water bath container and add the tenderloin. With those in place, fill the water bath with water to in between the minimum and maximum fill lines.
Heat a cast iron skillet over high heat. Once smoking, add the ghee to the skillet. Once melted, add the tenderloin and sear on all sides for 30 seconds to 1 minute, until browned.