This is my answer to your question from the general topics board....which should be here instead...
There was a thread about a few months back, but I couldn't find it for you...this is what I do, and it always comes perfect. I agree with the other poster, let your steaks come to room temp, not super cold from refrig, but certainly not warm either. I usually make lamb steaks, but it will work the same way for sirloin. First preheat oven to 375'. I make sure the steaks are absolutely dry, after of course you have already rinsed them, then I use garlic/pepper mixture on both sides, I put canola oil into a creuset frying pan (an enameled frying pan, is what works best, stay away from non stick, or stainless pans)..when the oil is very hot, but do not put the flame on super high, an enameled pot, gets very hot on med-hi and retains that heat quickly...so, once the oil is hot (do not use olive oil, you cannot sear at high temp with it, it burns)..
put the steaks in, and sear them for 4 min each side, turning once. There is something else I do that I really like and is optional, but
I put some chopped scallions in the pan when I'm searing because they get really carmelized and delish, so I then add these to the next step. Then with a seperate baking dish, I use a creuset enameled baking dish, and I then put the steaks in it, and I put rosemary olive oil all over the steaks, some fresh rosemary twigs under each steak, add my scallions and sometimes mushrooms also, and put them in my preheated 375' oven for about 15 min for rare-med, and 20-25 for med-well. They are always tender and juicy inside, and properly seared but not burnt on outside. Perhaps this will work for you,,,,i really feel the pan makes the difference. Good luck, let us know if it improved!