Remove the beef tenderloin from the fridge and unwrap. Pat any excess moisture from the exterior of the roast, then season it on all sides with the salt and pepper.
Let the roast rest, uncovered, on the counter to come to room temperature prior to cooking, 2 - 2 1/2 hours.
When the beef tenderloin is fully rested, preheat the oven to 450 degrees F.
In a large heavy-bottomed skillet (I like to use my 13-inch Lodge cast iron skillet) over medium high heat, add a generous swish of olive oil.
2-3 tablespoons olive oil
When the oil is nicely hot and shimmering, place the seasoned tenderloin into the oil, meat-side down (fat-side facing up). Brown the tenderloin roast for a just few quick minutes on all sides until it is deep golden brown with a nice, crusty exterior.
Slather the prepared butter mixture over the top side of the seared beef tenderloin, then place the skillet with the roast into the preheated oven on the center oven rack.
Roast the beef tenderloin for 30 minutes at 450 degrees F.
Reduce the oven temperature to 325 degrees F., continuing to cook the tenderloin for an additional 20-30 minutes at this lower temperature. At the 20 minute mark, use an instant-read meat thermometer probe to begin checking the internal temperature of the tenderloin to be sure it is on track for reaching 125 degrees F at the center.
When the beef tenderloin reaches 125 degrees F. at the center, remove it from the oven. Cover the pan tightly with foil, letting the roast rest for 15-20 minutes, allowing the tenderloin to continue to raise in temperature at the center to 130-135 degrees F. for medium rare doneness. **Keep in mind that if the beef tenderloin rested properly at room temperature before you seared it and began the roasting process (as directed in Step 2), the tenderloin will only need approx. 12-13 minutes per pound of total cooking time. Beef cooks much more quickly if it is not ice cold when you begin the cooking process.
Uncover the rested tenderloin and place it onto a large cutting board. Carve the tenderloin roast across the grain into thick slices.