Slow-Roasted Beef Tenderloin

Ingredients

• 1 center-cut trimmed beef tenderloin, 2 to 3 pounds
• Kosher salt and freshly ground black pepper
• 4 tablespoons unsalted butter
• 4 sprigs thyme
• 1 shallot, roughly sliced
• Finely minced chives, for serving
• Coarse sea salt, such as fleur de sel or Maldon, for serving
• 1 recipe Horseradish Cream Sauce, for serving

Directions

1. Use butcher's twine and butcher's knots to tie the tenderloin at 1-inch intervals. Be generous with the salt and pepper. Set it on a wire rack inside a rimmed baking sheet lined with foil, then leave it uncovered in the refrigerator overnight at a minimum, or for up to 2 nights.
2. When you're ready to cook, move an oven rack to the middle position and heat the oven to 225 degrees F, or 107 degrees C. Put the whole setup, baking sheet, rack, and tenderloin, into the oven. Roast until an instant-read thermometer inserted in the meat reads between 120 degrees F and 125 degrees F, or 49 degrees C to 52 degrees C; plan on 2 to 3 hours. Take the tenderloin out and give it 10 minutes at room temperature. Snip off the twine and pull it away.
3. If you're finishing under the broiler, move the rack so it sits 6 inches from the broiler element, then turn the broiler to high. Set a medium skillet over high heat and warm the butter, swirling the pan, until the foaming settles and the butter is pale brown and nutty. Add the thyme and shallots, and stir until the crackling quiets down. Pour the butter mixture over the tenderloin, using a spoon to spread it over every side. Pick the shallots off the top of the meat. Slide the pan with the tenderloin under the broiler and cook, turning the roast every 30 seconds, until the outside is well browned all around and the center reaches the rare mark, 125 degrees F (52 degrees C), or the medium-rare mark, 130 degrees F (54 degrees C), about 2 minutes total. Then continue with the resting, slicing, and serving.
4. If you're finishing on the stovetop, set a medium skillet over high heat and warm the butter, swirling the pan, until the foaming settles and the butter is pale brown and nutty. Put in the tenderloin along with the shallots and thyme, then cook, turning it occasionally and spooning the hot butter and aromatics over the roast as you go. Stop when the meat is well browned all around and the center reaches the rare mark, 125 degrees F (52 degrees C), or the medium-rare mark, 130 degrees F (54 degrees C), about 1 1/2 minutes.
5. Move the tenderloin to a cutting board and let it rest for 5 minutes. Cut it into 1/2-inch slices, shower with chives and coarse sea salt, and serve with Horseradish Cream Sauce.