Things You'll Need
A beef tenderloin is also called a whole fillet. It can be cut down to a fillet mignon, which is triangle-shaped and comes from the center of the tenderloin. The thicker and heavier a tenderloin is, the longer it takes for the center to reach the appropriate temperature. A 10 lb. tenderloin will generally need to cook for two hours or more, depending on how you prefer the steak to be cooked. There are many ways you can cook a whole tenderloin, but certain basic steps are required no matter what recipe you have chosen to use.
Season the tenderloin prior to roasting it. Since it is already a tender portion of meat, you can just use salt and pepper. You can use other seasonings according to your preference.
Preheat the oven to at least 500 degrees Fahrenheit. Cook the tenderloin until it reaches the internal temperature for the level of doneness you prefer. For rare, the temperature should be between 120 and 125 degrees Fahrenheit. Medium rare should be 130-140 degrees Fahrenheit, medium is 150-160 degrees Fahrenheit, medium well is 150 to 160 and well done is anything over 160 Fahrenheit.
Cover the roast with foil and let it sit for 20 minutes before serving. To serve, simply cut across the grain in 1/2 inch slices.
If your oven does not brown the meat sufficiently, you can put it in the broiler for the last 10 minutes.