Place the beef on a sheet pan and pat the outside dry with a paper towel. Spread the butter on with your hands. Sprinkle evenly with the salt and pepper. Roast in the oven for exactly 22 minutes for rare and 25 minutes for medium-rare.

Remove the beef from the oven, cover it tightly with aluminum foil, and allow it to rest at room temperature for 20 minutes. Remove the strings and slice the fillet thickly.