Beef Tenderloin with Horseradish Crust, Roasted Potatoes, and Garlic

Place a rack in the middle of the oven and preheat to 400 degrees F.

Place the potatoes in a large roasting pan and toss with 1 tablespoon of the oil, the rosemary, and salt and pepper to taste. Roast for 30 minutes, tossing them once or twice, or until beginning to brown, but not cooked through. Remove and set aside.

While the potatoes are roasting, place the horseradish in a fine-mesh strainer and drain off any liquid.

Season the beef on all sides with salt and pepper and the thyme.

In a large skillet, heat 2 tablespoons of the oil over high heat. Sear the meat on all sides, about 2 minutes per side, reducing the heat if the meat starts to burn. Remove from the heat and let cool thoroughly. (The meat and potatoes can be prepared several hours ahead of time up to this point. Cover and refrigerate until ready to roast. Be sure to remove the meat 15 to 20 minutes before roasting to bring the meat to room temperature.)

Preheat the oven to 425 degrees F. Place the meat on a roasting rack inside the roasting pan. The potatoes can either go underneath the beef (they will be basted with the beef juices) or you can push them off to the sides. Pat the mustard on top of the tenderloin, and then top with the drained horseradish, pressing down to form a crust. Season with salt and pepper. Drizzle the remaining tablespoon of oil on top of the horseradish crust. Place the garlic next to the potatoes.

Roast the beef and potatoes on the middle shelf for 45 minutes to 1 hour, or until the internal temperature of the meat is 140 degrees F for medium-rare. (The temperature will continue to rise once you take the meat out of the oven.) Let sit for 5 minutes, loosely covered with foil, before carving. The garlic can be served whole or squeezed out of the skins and served alongside the meat and potatoes.