Preheat the oven to 450 degrees F (230 degrees C).
STEP 2
Take the Filet Mignon (4) out of the refrigerator about half an hour before cooking them (filet mignon should be 1"-1 1/2" thick).
STEP 3
In an ovenproof heavy skillet or cast iron pan, melt the Butter (1 tablespoon) over medium high heat.
STEP 4
Add the Button Mushroom (8 ounce) until they've given up their liquid and start to brown. Transfer the mushrooms to a bowl and set aside. (Can be made ahead).
STEP 5
Season both sides of the steaks with Kosher Salt (1/2 teaspoon) and Ground Black Pepper (1/2 teaspoon).
STEP 6
In the same skillet, heat the Butter (1 tablespoon) over high heat until foamy and add the steaks to the skillet. Sear the meat on one side for about 2 minutes.
STEP 7
Use a pair of tongs to flip the steaks. Cook for an additional 1 1/2 to 2 minutes (for medium rare).
STEP 8
Then transfer to the hot oven and cook for 2-3 more minutes for medium rare.
STEP 9
Remove the skillet from the oven and transfer the steaks to a cutting board or serving platter to rest for five minutes before serving.
STEP 10
While the steak rests, heat the Bordelaise Sauce (1 cup) and stir in the mushrooms.