On the night before cooking, make the marinade. Combine the garlic, olive oil, salt and pepper in a blender or food processor. Blend to a thick paste. Spread the marinade on the tenderloin and refrigerate overnight. Remove from the refrigerator a couple of hours before you plan to cook it to bring to room temperature. Preheat the oven to 450 degrees. Place the filet on a rack and roast 30 minutes for rare, 40 minutes for medium-rare, and 50 minutes for medium well. Remove the filet from the oven, place it on a plate, cover with foil and let rest for 10 to 15 minutes. Cut the beef crosswise into thin slices and transfer to a serving platter. Garnish with whole roasted heads of garlic if you like. You can serve the filet warm or at room temperature.
Makes 10 to 12 servings.