One day ahead of serving:
Rinse the tenderloin with cool water and pat dry with paper towels. Generously season with salt, pepper, and rosemary. Wrap the tenderloin in plastic wrap and refrigerate for at least 8 hours.
Preheat oven to 450 degrees. Remove the wrapping from the tenderloin and place in a shallow roasting pan. Cook for 40 minutes for medium rare. Remove the tenderloin from the oven, cover with foil and let rest 10 minutes. Slice thinly to serve.
Makes 8 to 14 servings