Follow these clear steps to create the amazing Oven Roast Beef Tenderloin with Horseradish-Mustard Sauce:

1. Preheat your oven: Set the oven to 425°F (220°C) to prepare for roasting.

2. Prepare the beef: Remove the beef tenderloin from the refrigerator about 30 minutes before cooking. This allows for even cooking. Pat it dry with paper towels.

3. Season the tenderloin: Rub the beef with olive oil, salt, and pepper. Then sprinkle the chopped rosemary evenly over the surface.

4. Sear the beef: In a hot skillet, sear the tenderloin on all sides for about 2-3 minutes per side until browned. This step locks in the flavor.

5. Transfer to baking pan: Place the seared tenderloin on a roasting pan or baking sheet.

6. Roast in the oven: Roast the beef in the preheated oven for about 25-30 minutes or until the internal temperature reaches 135°F (57°C) for medium-rare doneness.

7. Prepare the sauce: While the beef is roasting, mix together the Dijon mustard, horseradish, sour cream, and lemon juice in a small bowl. Adjust seasoning with salt and pepper to taste.

8. Rest the meat: Once the beef reaches the desired temperature, remove it from the oven and let it rest for 10-15 minutes. This allows the juices to redistribute.

9. Slice and serve: After resting, slice the beef into 1-inch thick slices. Arrange on a serving platter.

10. Drizzle with sauce: Serve the beef slices with a generous spoonful of horseradish-mustard sauce over the top. Garnish with fresh herbs if desired.

These steps will guide you through crafting a delicious oven roast that’s succulent, tender, and full of flavor!