CUT: One end of the beef tenderloin will have a thinner tapered end - we will be folding this end up against the roast. Cut the beef tenderloin in half so the two halves will be roughly equal length when you fold the thin end up against the roast to create a uniform cylinder shape (see photos in post).
TIE: In order for beef tenderloin to cook evenly and hold the folded tail in place, it is tied with kitchen twine – you can also ask a butcher to do this for you. First, re-fold the thin end up against the roast to create a uniform cylinder shape if needed. To tie, you can simply tie individual loops spaced 1 ½ inches apart down the length of each tenderloin and then one loop going around the roasts lengthwise or I’ve detailed the proper technique below which is actually quicker (just maybe more difficult explain, so just try it! – see detailed photos in post):
Take a string and loop it around the width of one roast, about 1-inch from the end and tie a snug knot. Loop the string around your left hand by moving the string from the front of your hand to the back so it creates a loop. With your looped hand, pick up the front of your roast and pull the loop around your roast. Shimmy the loop down to create a loop 1 ½ inches from the first loop. Pull any loose string so it’s snug and repeat the process, tightening as you go. To finish, wrap the string all the way around the roast lengthwise then tie off the end and trim any excess string.
SPICE RUB: Whisk together all of the Spice Rub ingredients in a small bowl; set aside. Pat roasts dry with paper towels then evenly rub spice mix all over (it will seem like a lot but use all of it).
BRING TO ROOM TEMPERATURE: Let roasts rest at room temperature for two hours or transfer to the refrigerator to rest uncovered for up to 48 hours. If the beef is refrigerated, let it sit at room temperate for 2 hours before cooking.
HORSERADISH CREAM SAUCE: At any point while the roast is resting, mix all of the Horseradish Cream Sauce ingredients together in a medium bowl. Cover and refrigerate until ready to use. When ready to use, taste and adjust to taste if desired.
GARLC HERB BUTTER: When ready to cook, preheat the oven to 450 degrees F. Meanwhile, mix all of the butter spread ingredients together in a bowl until evenly combined; set aside.
SEAR ROAST: Heat 2 tablespoons vegetable oil in a large cast iron skillet over medium high-heat. When the oil is very hot and just smoking, add beef tenderloin roasts (you may need to work in batches). Sear each side of beef until deeply browned. Transfer to a plate and wipe out any blackened drippings. Drizzle skillet with oil and transfer roasts back to the skillet. Slather the butter spread all over the tops and sides of the roasts (use all of it).
BAKE: Transfer the skillet (or use a lightly greased baking dish/roasting pan) to the preheated oven. Bake at 450 degrees F until beef registers desired doneness: between 120-125°F for medium rare, recommended (about 20-25 minutes) or 115-120°F for rare or 130-135°F for medium rare. **Keep in mind the beef will rise 5-7 degrees after resting, so take the meat out of the oven 5-7 degrees below the temperature you are aiming for. You will likely need to remove one roast before the other.
REST AND SLICE: Remove skillet from the oven and baste roasts several times with the buttery juices from the skillet, then transfer roasts to a cutting board and tent loosely with foil. Let beef rest for 15 minutes before slicing into ½-inch thick slices. Serve with Horseradish Cream Sauce.