The sirloin sub-primal yields about 11 different cuts, with most of them sold as only "sirloin." If you're lucky enough to get a descriptive name, you at least have an idea of which cooking method to use. Tough cuts, such as ball tip, do best with moist heat, while others, such as top sirloin, do fine with a quick pan-fry. But if you have an ultra thin sirloin, which measures under 3/4-inch thick according to food-service standards, the cut doesn't matter, because you cook them all the same way: fast. You have to move fast and use lesser-known techniques to avoid overcooking an ultra thin sirloin.
Wrap the ultra thin sirloin tightly in plastic wrap and place it in the freezer. Leave the sirloin in the freezer for about one to two hours, depending how cold and crowded you freezer is. You want the sirloin frozen throughout.
Heat 3 or 4 tablespoons of high-temperature fat in a heavy bottomed pan or skillet over medium-high heat. Peanut oil, soybean oil and clarified butter have moderate to high smoke points.
Remove the sirloin from the freezer while the oil heats and unwrap it. Place the sirloin in the pan when the oil starts to shimmer. Expect a lot of sizzle when you place the sirloin in the oil. You can use tongs to lay the steak in the pan if you like.
Flash-fry the sirloin for 1-1/2 minutes on each side for medium-rare, and 1-1/2 to 2 minutes on each side for medium. Anything longer than four minutes total and you have a well-done sirloin. Don't touch the steak while it cooks except to turn it over once after about 1-1/2 minutes of cooking. The more you move the steak, the lower the temperature of the fat drops, which throws off the whole flash-frying dynamic.
Remove the steak from the pan with tongs and place it on a plate lined with paper towels. Season the steak to taste on both sides with kosher salt and freshly ground black pepper as soon as you lay it on the paper towels.
Wrap the ultra thin sirloin tightly in plastic wrap and place it in the freezer. Leave the sirloin in the freezer for about one to two hours, depending how cold and crowded you freezer is. You want the sirloin frozen but not solid all the way through.
Place the broiler pan at the top position in the oven. Set the oven to Broil.
Remove the steak from the freezer and unwrap it. Place the steak on a slotted broil pan and place it on the top oven rack.
Broil the sirloin for 1-1/2 minutes and turn it over with tongs. Broil another 1-1/2 minutes for medium rare, and another 2 minutes for medium. Broil the steak for any longer than 3 to 3-1/2 minutes total and you have a well-done.
Remove the steak from the oven and season it with kosher salt and freshly ground black pepper.