Warm steaks to room temperature. Do not puncture steaks to tenderize. Season with salt and ground black pepper.
Heat your oil, butter and seasonings in your cast iron skillet. Add your thick sliced onions and fry for about 2 minutes on a higher heat. Don't cover and allow to steam or allow your onions to fry for too long. However, do allow your onions to char a bit on their edges. You'll want your onions slightly trasparent and somewhat crispy [or a snap] at serving.
Add your thick sliced Portabella Mushrooms, mix well and fry for another minute or two. Your mushrooms will cook and absorb your pan seasonings VERY quickly - so concern yourself more with the crisp or snap of those onions. The second picture shown below is 1 minute in to its fry and stir time. Notice how the mushrooms are already almost limp, yet the onions still look as though they have some life [or chew] to them.
Drain onions and mushrooms on quality, lint free paper towels.
Fry your thin T-Bones on high [and I mean smokin' hot] in that same cast iron skillet and seasoned oil with a lid. Fry for 1 minute or less on each side for rare. Just a bit longer for medium rare and 2 minutes on each side for well done. Remember, these are thin steaks on a high heat. They fry fast! Also, try to put a slight char on your steaks by waiting the full 1 or 2 minutes to flip them. You can slightly lift the edges to peek for burning, but no more if you want that delicious char.
Drain steaks on top of your cooked onions and mushrooms that are resting on your paper towels for a few minutes. After they sit, plate your steaks and pile your vegetables on top. Garnish with fresh or Dried Parsley. You can also pre-make and have on hand, my delicious, basic garlic butter to serve atop your hot steaks. This is always an appreciated option and this garlic butters shelf life - is darn near forever! You can also put this butter on baked potatoes.
Enjoy!
