A perfect steak has a well-developed crust encapsulating soft, juicy meat. One of the easiest, most effective ways to accomplish this perfection is pan-searing a high-quality steak, then finishing it in the oven. A sirloin filet is exceptionally flavorful, and its natural tenderness and the thickness of this medallion-shaped cut make it ideal for this mode of preparation. This technique is well-worth mastering for home cooks, as it's an easy way to cope successfully with thick steak and chop-style cuts of beef, pork and other meats.
Take the sirloin filets out of the refrigerator 45 to 120 minutes before you plan to cook them; chilled beef doesn't cook evenly. Season the steaks liberally as soon as you take them out with a coarse-grained salt. This provides enough time for the salt to pull out and flavor moisture from the beef, and for the moisture to be reabsorbed.
Preheat the oven to 500 degrees Fahrenheit for about the last 30 minutes of keeping the meat at room temperature.
Place a large cast-iron or other heavy-bottomed, oven-safe pan on a burner over medium-high heat for at least several minutes. Wait for it to get so hot that when you flick water into it, the drops sizzle and evaporate right away. Then, add in a minimal film of cooking oil and heat it until it has a watery consistency.
Put the sirloin filets in the pan without crowding them; sear them in batches if necessary. Don't move them for about 2 minutes, allowing them to sear undisturbed. Once they slide easily around with a gentle shake of the pan, turn them over with tongs. Sear the second side of the steaks for about 1 minute; transfer the pan into the oven.
Cook the sirloins in the oven to 5 degrees below your final target temperature, as these thick cuts continue to cook another 5 degrees during resting. Insert an instant-read thermometer into the center of the filets to determine doneness. The U.S. Department of Agriculture advises cooking solid cuts of beef to 145 F, which puts it basically at the border between medium and medium-well; a final temperature of 120 F equals rare; 130 F is medium-rare; 140 F is medium; 150 F is medium-well and 160 F is well done. Expect a sirloin filet to take about 5 or 6 minutes in the oven for medium.
Remove the sirloin filets from the pan promptly to avoid overcooking them. Put them on a large plate to rest for at least 5 minutes. Their internal temperature rises about 5 degrees during resting, and their juices, which are released during cooking, are reabsorbed by the muscle fibers, preventing the loss of valuable juiciness.
Never leave steak or other meat out at room temperature for more than 2 hours, or it experiences dangerous bacterial growth that can easily lead to food poisoning.