01 - Pat steaks completely dry with paper towels. Generously season both sides with kosher salt and freshly ground black pepper.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Sear steaks for 3-4 minutes per side for medium-rare doneness, or adjust timing to your preference. Transfer to a plate and tent loosely with aluminum foil to rest.
03 - Reduce heat to medium. Add butter to the same skillet and 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, stirring to combine and coat the vegetables evenly.
06 - Carefully pour in brandy or cognac. If desired, use a long match to carefully flambé and burn off the alcohol. Exercise extreme caution when attempting this step.
07 - Add beef broth and simmer for 2 minutes, using a wooden spoon to scrape up any browned bits from the bottom of the skillet.
08 - Pour in heavy cream and stir to incorporate. Simmer for 2-3 minutes until sauce thickens slightly and coats the back of a spoon.
09 - Return steaks along with any accumulated juices to the skillet. Spoon the creamy mushroom sauce over the steaks and heat through for 1 minute.
10 - Sprinkle with freshly chopped parsley and serve immediately while hot.