Remove the beef tenderloin from the refrigerator 45–60 minutes before cooking to allow it to come to room temperature. This ensures even cooking from edge to center.

Pat the tenderloin completely dry with paper towels. Combine the minced garlic, rosemary, and thyme with the olive oil to form a paste. Rub this all over the surface of the tenderloin, then season generously on all sides with kosher salt and cracked black pepper, pressing firmly so it adheres.

Preheat your oven to 425°F (220°C). Heat a large oven-safe skillet or cast iron pan over high heat until very hot and just beginning to smoke.

Add the tenderloin to the dry pan (no extra oil needed) and sear for 2–3 minutes per side, turning to brown all sides evenly, including the ends. This takes about 8–10 minutes total and builds a deep, flavorful crust.

Transfer the seared tenderloin (still in the skillet) to the preheated oven. Roast for 20–25 minutes, or until an instant-read thermometer inserted into the thickest part reads 125–130°F for medium-rare.

Remove from the oven, tent loosely with foil, and rest for 15 minutes. The internal temperature will rise to 130–135°F during resting. Do not skip the rest — it is essential for juicy slices.

While the tenderloin rests, whisk together the sour cream, prepared horseradish, mayonnaise, Dijon mustard, and fresh lemon juice in a small bowl. Season with salt and pepper to taste. Fold in chives if using.

Taste and adjust — add more horseradish for extra punch, more lemon for brightness, or a pinch of salt to pull the flavors together. Cover and refrigerate until ready to serve.

Remove the kitchen twine from the rested tenderloin. Using a sharp carving knife, slice into 3/4-inch rounds. Arrange on a serving platter and spoon some of the horseradish cream sauce alongside. Serve remaining sauce in a bowl at the table.