01 - Pat steaks thoroughly dry with paper towels. Season both sides generously with kosher salt and freshly ground black pepper.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Place steaks in the pan and sear for 3-4 minutes per side for medium-rare doneness, or adjust timing to your preference. Transfer steaks to a clean plate and tent loosely with aluminum foil to rest.
03 - Reduce heat to medium. Add butter to the same skillet and let melt. Add sliced mushrooms and sauté until golden brown, approximately 5 minutes.
04 - Stir in chopped shallots and minced garlic. Cook for 1 minute until fragrant, being careful not to burn the garlic.
05 - Add Dijon mustard and Worcestershire sauce to the skillet, stirring to incorporate with the mushrooms and aromatics.
06 - Carefully pour in brandy or cognac. If desired, carefully ignite with a long match to flambé and burn off the alcohol. Exercise extreme caution when performing this step.
07 - Pour in beef broth and let simmer for 2 minutes, using a wooden spoon to scrape up any browned bits from the bottom of the pan.
08 - Stir in heavy cream and continue simmering until the sauce thickens slightly, about 2-3 minutes.
09 - Return steaks and any accumulated juices to the skillet. Spoon the creamy mushroom sauce over the steaks and heat through for 1 minute. Sprinkle with fresh chopped parsley and serve immediately.