1. Preparing the Tenderloin: Trim any excess fat or silverskin from the beef tenderloin. Cut the tenderloin into two even pieces and tie with butcher’s twine to maintain shape and ensure even cooking. Season all sides generously with salt and black pepper. Allow the tenderloin to rest at room temperature for about 2 hours to ensure even cooking.

2. Prepping the Oven and Pan: Preheat your oven to 425°F (220°C). Heat 2 tablespoons of olive oil or avocado oil in a large cast-iron skillet over medium-high heat until the oil shimmers.

3. Searing the Tenderloin: Place the tenderloin pieces into the hot skillet and sear for 3-5 minutes on each side until a golden-brown crust forms. Rotate gently using tongs to ensure even searing on all sides.

4. Preparing the Garlic-Herb Butter: In a small bowl, mix 4 tablespoons of softened salted butter with minced garlic, prepared horseradish (or Dijon mustard), and minced rosemary or thyme to create a fragrant and flavorful butter mixture.

5. Roasting the Tenderloin: After searing, remove the skillet from heat and spread the garlic-herb butter mixture evenly over the tenderloin. Insert a probe thermometer into the thickest part of the beef and place the skillet in the preheated oven. Roast for 20-25 minutes, monitoring the internal temperature for desired doneness: Rare: 115°F – 120°F, Medium-Rare: 120°F – 125°F, Medium: 130°F – 135°F, Medium-Well: 145°F.

6. Resting the Tenderloin: Remove the tenderloin from the oven and transfer it to a cutting board. Tent loosely with aluminum foil and let it rest for 15-20 minutes to allow the juices to redistribute for maximum tenderness and flavor.

7. Slicing and Serving: Slice the tenderloin gently into 1-inch-thick slices using a sharp knife. Serve with accompaniments such as creamy horseradish sauce, mashed potatoes, or roasted vegetables for a sumptuous and elegant meal.