Boneless butt tenderloin is the thickest end of the tenderloin, which is a long fillet cut from a loin of beef. It is so-named because the meat is very tender, making it suitable as cuts of beef roast or steak. Since this cut is taken from muscle that generally doesn't get much of a workout, it's not necessary to cook the meat with moist heat, a method reserved for less tender cuts. Whole-muscle meat, like boneless butt tenderloin, can be safely cooked to lower internal temperatures than some other cuts. This cut of beef is usually served medium rare.
Preheat the oven to 425 degrees Fahrenheit. Check the racks to see if you need to make any adjustments or remove the top rack. Boneless butt tenderloin averages between 2 lbs. and 7 lbs., but a larger cut may need more space in the oven cavity for heat to circulate. The shape and size of your roasting pan is another factor to consider.
Prepare the tenderloin. If necessary, "peel" the meat. This means to carefully remove excess fat and the "silver skin" -- the connective tissue that surrounds the loin muscle.
Season the tenderloin with salt and pepper. For best flavor, use sea salt and freshly cracked black pepper. You can flavor with meat with other seasonings, such as dried sage, rosemary or thyme.
Place the seasoned tenderloin into the roasting pan and set in the hot oven, without adding water or a cover to the pan. Since this portion of beef is a premium cut, it can withstand fast cooking under dry heat at a high temperature. The smoky flavor and tender texture achieved from this method of cooking is produced by the Maillard reaction, a process during which proteins and sugars break down.
Roast the tenderloin for 45 to 60 minutes, or until the meat reaches an internal temperature of 145 degrees Fahrenheit for medium rare.
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Let the tenderloin rest for 15 to 20 minutes when it's finished cooking. The proteins in the muscle reabsorb the natural juices in the meat, which would otherwise be lost if you cut into it right away.
If the meat was frozen, let it thaw completely before cooking. The U.S. Department of Agriculture recommends thawing beef in the refrigerator. Once beef is defrosted, you can keep it refrigerated for three to five days before cooking.