Sprinkle all sides of the tenderloin with sea salt and place in a casserole dish or large tupperware container. Refrigerate up to 12 hours, uncovered.

Add 3 to 4 tablespoons of avocado oil (or high temperature cooking oil of choice) to a cast iron skillet and heat to medium-high. Allow the skillet to heat to a high temperature (about 375 to 390 degrees F, which you can check if you have a laser thermometer).

Preheat the oven to 425 degrees Fahrenheit.

Transfer the beef tenderloin to the hot skillet and sear for 3 to 4 minutes per side on all 4 sides, or until the whole tenderloin has a golden-brown crust on the outside.

Place the skillet to the preheated oven and roast to desired doneness, using a thermometer to check the internal temperature - 115°F to 120°F for rare (about 10 to 15 minutes), 120°F to 125°F for medium-rare (about 12 to 18 minutes), and 130°F to 135°F for medium (about 18 to 25 minutes). Keep in mind, the temperature of the meat continues to raise once it’s out of the oven. It will increase by 5 to 10 degrees as it sits.

Remove the tenderloin from the oven and place it on a cutting board to rest for 15 minutes.

Cut the strings off of the roast and slice into 1/2-inch slices. Serve and enjoy!