With the rack in the middle position, preheat the oven to 500°F (260°C). Line a baking sheet with foil.
In a bowl, combine all of the ingredients, except for the roast.
On a work surface, rub the roast all over with the seasoning mixture.
Place the roast on the baking sheet, fat side up. Bake for 25 minutes. Turn the oven off and do not open the door for 2 hours. It is very important not to release any heat from the oven. Remove the roast from the oven and slice. Serve with béarnaise sauce, if desired.
For 6 people: 4 ½-lb (2 kg) roast, cooking time at 500°F (260°C) = 25 minutes For 10 to 12 people: 8 lb (3.6 kg) roast, cooking time at 500°F (260°C) = 40 minutes For 14 to 16 people: 11 lb (5 kg) roast, cooking time at 500°F (260°C) = 55 minutes