01 - Pat steaks thoroughly dry with paper towels. Season both sides generously with kosher salt and freshly ground black pepper, pressing gently to adhere.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Place steaks in the pan and sear for 3 to 4 minutes per side for medium-rare doneness, adjusting time to preference. Transfer steaks to a warm plate and tent loosely with aluminum foil to rest.
03 - Reduce heat to medium. Add butter to the 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 pan, stirring to combine with the mushroom mixture.
06 - Carefully pour in brandy or cognac. If desired, carefully ignite with a long kitchen match to flambé and burn off 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 sauce thickens slightly, about 2 to 3 minutes.
09 - Return steaks and any accumulated juices to the skillet. Spoon the creamy mushroom sauce generously over the steaks and heat through for 1 minute. Garnish with fresh chopped parsley and serve immediately.