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Cut the fat and silver skin. Use your fingers to break through the connective tissue joining the fat to the meat. Then use a sharp knife to completely slice it off. Trim off the silver skin too. Avoid blunt knives because they can lead to sudden, dangerous movements. Use cooking/butcher’s twine to wrap up the tenderloin. Tighten it in areas where the meat is thicker so that the entire cut is an even thickness. This is the only way to ensure proper cooking throughout.
Prep, sear, and baste
Preheat the oven. Sear the seasoned tenderloin until lightly brown. Add the butter, garlic, and thyme to the skillet to baste the tenderloin.
Roast and let rest
Transfer the skillet to the oven and roast for 35-40 minutes. Remove it from the oven. Place it on a cutting board to rest.
Mix the parsley, basil, and thyme in a small bowl. Press the herb mixture into the tenderloin until it’s completely coated. Prepare the sauce. Whisk the mayo, horseradish, mustard, and garlic in a small bowl until smooth. Slice the beef tenderloin and serve it with horseradish sauce on top. Enjoy!