Season the filets with half of the salt and all of the crushed black peppercorns, pressing the pepper gently into the meat to ensure it adheres.

Heat a cast iron pan over medium-high heat and add 2 tablespoons of butter. Once the butter has melted and is sizzling, add the steaks to the pan.

Sear the steaks for about 1-2 minutes on each side until they sear nicely on both sides, they should be cooked rare at this point. Once seared, remove the steaks from the pan and set them aside to rest.

In the same pan, add the remaining 2 tablespoons of butter. Once melted, add the chopped shallots and sauté them until they become translucent.

Add the sliced button mushrooms and the remaining salt to the pan and add the dried thyme. Cook until they are browned and tender, stirring occasionally.

Pour in the red wine with the mushrooms, deglaze the pan using a wooden spoon to scrape up any flavorful browned bits from the bottom.

Stir in the beef stock and bring the mixture to a simmer. Allow the sauce to reduce and thicken slightly for about 5-7 minutes, seasoning with additional salt to taste if needed.

Return the seared steaks to the pan, ensuring they are well-coated with the sauce, and let them finish cooking to your desired doneness, about 2-4 more minutes.

Serve the steaks hot, generously drizzled with the rich, savory mushroom sauce. For a complete meal, pair the Steak Diane with creamy mashed potatoes. Enjoy!