whenever I hear the term "wild mushrooms", I think of a cartoon I once saw many years ago. There are two bins in the supermarket. One bin says "Wild Mushrooms - $5/lb", the other bin says "Wild Mushrooms? - $.05/lb".
The ideas above are all good. I pan sear the steaks 3 minutes to a side, and then pop into a 450 F oven for 8 minutes for medium rare tenderloins.
Then I tent the steaks on a plate, and then to the empty cast iron skillet, I add 2-3 TBSP unsalted butter, and as many shallots/scallions/red onion/leeks/yellow onion finely diced as I desire. Cook just a bit, and add the roughly chopped fresh mushrooms. I like baby bellas.
When they lose their water, and most of it evaporates, I deglaze with a dry white wine, like Dry Zack from Spain. Its aged 15 years.
Then I add the demi-glace, usually about 1 cup for 2-3 steaks.
I season the sauce with S&P, and sometimes add alittle heavy cream for a change of pace. I have used red wine on occasion instead of the dry white wine, but I like drinking red wine so much, I never have any lying around to use!
You could even spice up the sauce a little more by soaking your coarsely cracked black and/or green peppercorns in the heavy cream before adding, if you choose to add cream. Always reduce to desired consistency of the sauce.
Much more additions, and the sauce becomes too complicated/complex in flavor.