12ouncessliced mushrooms, crimini, button, or stemmed shiitake
¾cuplow-salt beef broth or chicken broth
2tablespoonsfresh parsley, chopped, plus extra for garnish
1tablespoonfresh thyme leaves, plus extra for garnish
⅛teaspooncayenne pepper, optional
Salt and pepper, to taste
Drizzle 2 tablespoons olive oil on both sides of the steaks. Sprinkle both sides and edges generously with salt and pepper. Set aside 45 minutes to come to room temperature.
Meanwhile, prepare the sauce. Heat the remaining tablespoon of olive oil in a large skillet over medium-high heat. Add mushrooms and shallots and cook until they’re tender and caramelized, about 5 minutes.
Add the garlic and cook 1-2 minutes more, stirring frequently. Remove skillet from heat and stir in the sherry. (Caution: the mixture may ignite if cooking on a gas stove.)
Return skillet to the heat. Stir in the broth and mustard. Cook 2 minutes.
Add the cream, parsley, thyme, and cayenne (optional). Simmer until the sauce is slightly thickened, about 5 minutes. Season to taste with salt and pepper.
Turn heat to a very low setting just to keep the sauce warm while cooking the steaks.
TO GRILL: Prepare grill over high heat. Grill steaks until cooked to desired doneness, 5-6 minutes per side for medium-rare (see note). To get crisscross grill marks, turn steaks with a spatula 90 degrees halfway through the cooking time for each side. Transfer filets to platter and let rest 5 minutes. Serve with sauce.
TO PAN SEAR AND ROAST: Preheat oven to 425°F. Heat oven-proof pan coated with 2 tablespoons of olive oil over medium-high heat. Sear steaks 3 minutes per side. Transfer pan to preheated oven and roast for 8-10 for medium rare. Let steaks rest 5 minutes. Serve with sauce.
Note: for reference, 125-130° for medium rare; 135-140° for medium, 150° and above for well done. Invest in a good-quality, instant-read meat thermometer to keep guessing to a minimum.