Sirloin roasts are comparatively lean, tender, flavorful and cost-effective cuts of beef -- an ideal cut for traditional pot roast. Since they are tender, they benefit from dry-heat cooking methods such as oven-roasting and grilling. Due to the larger size of a roast, the indirect heat of an oven is the recommended cooking method for a sirloin roast rather than the direct heat of a grill, which is more difficult to regulate.
Trim and Season the Roast
Trim the tough, silver connective tissue off the surface of the meat with a sharp, flexible knife such as a boning knife. Remove thick patches of fat from the surface, as well. It is fine to leave thin or narrow bands of fat. Season the roast with salt, pepper, herbs and spices, such as thyme, rosemary, cayenne, dry mustard or garlic powder. Place the roast on a plate or pan, cover it with plastic wrap, and rest it at room temperature for one to two hours. Room temperature meat browns more effectively than cold meat.
Brown the Surface
Add olive oil to a deep skillet or pot preheated on the stove to medium heat. Place the seasoned roast in the oil to brown the surface. Browning the roast enhances the flavor and prevents moisture loss. Turn the roast once the underside is a rich caramel hue and repeat the process until all of the sides are browned. To reduce cleanup, use a skillet or pot that is ovenproof so that you can brown the meat on the stove then roast it in the oven without changing pans.
Transfer to the Oven
Add vegetables such as potatoes, onions, carrots, celery or peppers to the pan, if desired. You can also pour a small amount of wine or beef stock to enhance the flavor and deglaze the bottom of the pan. Place the roast in a 325-degree Fahrenheit oven. Do not cover the meat while it roasts.
Cook to a Safe Temperature
Roasting time depends on the type of sirloin cut and its size. A tri-tip roast, which is a smaller cut, cooks in about 30 to 40 minutes. Other sirloin roasts generally cook in 16 to 21 minutes per pound. Check the internal temperature of the roast with a meat thermometer to determine precisely when it is done. Beef roasts must be 145 F to be safe to eat, according to the United States Department of Agriculture. Ambient heat continues to cook the meat after you remove it from the oven, raising the internal temperature five to 10 degrees. Therefore, you can remove the roast from the oven when it reaches 135 or 140 F, if you prefer a medium-rare roast. Remove the roast when it reaches 150 F for medium doneness, or wait until it is 160 F, if you want it well done. Food professionals recommend serving sirloin roast when it is medium rare.
Rest the Roast
Cover the roast with aluminum foil after you remove it from the oven. Rest it for five to 15 minutes before slicing or serving it. The juices start to thicken while the meat rests, prevent excessive moisture loss when you cut into the meat. Place the pan on the stove over medium-low heat to prepare a gravy with the drippings from the roast. Add flour to the juice in the pan to make a roux, then thin the mixture with milk or broth, whisking constantly.