A steakhouse roast, more commonly known as a strip loin roast, is taken from the tenderloin; this boneless cut is particularly well marbled with fat and, cooked properly, can be juicy, tender and flavorful. As the cook, your most important job is to prevent dried-out, tough, chewy meat resulting from overcooking. Cooking time is affected by several variables; while you should have an estimated cooking time in mind, go by the meat's internal temperature to know when it's ready to come out of the oven.
Remove the steakhouse roast from the refrigerator an hour before cooking it so it can come to room temperature. Chilled beef doesn't cook evenly, and the rapid change in temperature from fridge to oven causes the meat fibers to contract and toughen.
Trim excess fat off the strip loin roast with a sharp knife, leaving a layer of 1/4 to 1/2 inch of fat to flavor the meat as it melts during cooking. It's easiest to trim fat while the roast is still chilled.
Arrange the racks in your oven as needed so the steakhouse roast is in the middle of the oven during cooking. Preheat the oven to 450 degrees Fahrenheit.
Season the strip loin roast. The meat has plenty of flavor on it's own, so doesn't really need anything more than a patting of salt and pepper to bring those flavors out. Add a sprinkling of dried thyme or rosemary if you want a bit more depth of flavor.
Line the bottom of a shallow roasting pan with aluminum foil to protect it from burned-on drippings and to keep cleanup simple. Don't use a pan more than 2 inches deep, or you risk partially steaming the steakhouse roast. Put the rack in the pan and center the meat on it.
Put the strip loin roast into the middle of the oven and cook it for 15 minutes, then turn the oven down to 350 degrees F.
Cook the steakhouse roast to at least medium, or an internal temperature of 145 degrees F, as determined with use of a meat thermometer. Remove the meat from the oven once it reaches 140 degrees F; the internal temperature will rise at least another 5 degrees during resting.
Transfer the strip loin roast immediately to a serving tray, but don't start cutting it yet. Rest it for 15 minutes so its juices redistribute and settle rather than running out of the meat when it's cut. It will come to the safe minimum temperature during resting, provided it reached at least 140 degrees F in the oven. Tent it with aluminum foil to keep it warm for the meal.