Pat the meat dry. Place the roast, fatty side up, in a large roasting pan. Drape it with paper towels and let stand at room temperature for 2 hours. Preheat the oven to 500°F (260°C). Make sure to let it preheat for about 30 minutes.
Using the tip of a sharp knife, cut 10 to 15 small slits all over the roast. Insert the garlic slivers in the slits far enough so they do not protrude beyond the surface of the meat. Let it stand while the oven preheats.
Brush the meat all over with the butter or oil and season generously with salt. Place the pan in the center of the oven. Roast for 7 minutes per pound if using an electric oven, 6 minutes per pound if using a gas oven. Turn off the oven. Let the roast rest in the oven, without opening the door, for 2 hours. Take note of the internal temperature of the roast, inserting a thermometer into a cut side of the roast as close to the center as possible. This is very important. Then pour off any juices that have pooled in the pan and reserve.
Remove the roast from the oven. If you like your beef bloody rare, it’s probably ready now. If you like your beef anything but absolutely rare, sprinkle the top of the meat with a generous grinding of pepper and dust lightly with flour. Let it set at room temperature while you preheat the oven to 500°F (260°C).
When the temperature is reached, place the roast in the oven for 5 to 25 minutes, depending on the internal temperature you noted at the end of the resting period and how well done you like your roast. If the internal temperature was 125°F (52°C), warm the meat for 15 minutes; if it was 115°F (46°C) or so, warm it for 20 to 25 minutes. If after 10 minutes the pan drippings smell as if they are burning, reduce the oven temperature to 450°F (230°C).
Transfer the roast to a platter, tent loosely with aluminum foil, and let rest for 15 minutes.