If the sirloin is one piece, cut it in four equal sized steaks. If you have the time, apply a dry brine at least 2 hours before.
Heat up the oven to 110° C / 230° F. Place the steaks in an oven pan. Stick a thermometer in one of them to monitor temperature. Let them sit in the oven for roughly 20 minutes, the inner temperature should be 50° C / 122° F.
Take them out and let them rest for a few minutes. Pat them dry with a paper towel. It is very important with a dry surface when searing.
Turn on the stove, and use either a non-stick frying pan or a cast iron pan. Add the oil to the pan. Fry the steaks on high heat, make sure to flip them every 30 seconds. When the inner temperature reaches 55° C / 130° F they’re done.