1.Trim the beef tenderloin if it's not already, then cut in half to make two pieces. Tuck the long end under and use butcher's twine to tie the tenderloin. Season all over with 1 teaspoon salt, garlic powder, and pepper and leave in fridge, uncovered overnight, or at least 10 hours.
2.Remove tenderloin from fridge and set on counter for about 2 hours prior to cooking, to come to room temperature. Meanwhile, in a small bowl mix butter, 1/4 teaspoon salt, garlic, horseradish, rosemary, thyme, and parsley. Set aside.
3.Preheat oven to 425 degrees F. Place oil in a large cast-iron skillet and heat over medium-high heat. Sear the beef tenderloin on all sides and ends, about 3 to 5 minutes per side, creating a nice golden-brown crust. Transfer the tenderloin into a foil lined sheet pan.
4.Slather the seared tenderloin with the butter mixture and then insert a probe thermometer. Roast until desired internal temperature is reached, about 20 to 25 minutes. For rare take the roast out at 115°F-120°F, for medium rare 120°F-125°F, and for medium 130°F-135°F.
5.Remove tenderloin from oven and transfer to a cutting board. Tent with foil and let rest for 15 to 20 minutes to allow the juices to redistribute. Cut twine then slice into 1" slices. You may use the pan used to sear the tenderloin to make a red wine gravy.