01 - Pat steaks thoroughly dry with paper towels. Season both sides generously with kosher salt and freshly ground black pepper, pressing the seasoning into the meat.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Add steaks and sear for 3–4 minutes per side for medium-rare doneness, or adjust timing 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 same skillet and melt. Add sliced mushrooms and sauté until golden brown and moisture has evaporated, 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 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 during this step. Alternatively, simply simmer for 1 minute to evaporate alcohol.
07 - Pour in beef broth and simmer for 2 minutes, using a wooden spoon to scrape up any browned bits from the bottom of the skillet.
08 - Stir in heavy cream and continue simmering until sauce thickens slightly and coats the back of a spoon, 2–3 minutes.
09 - Return steaks and any accumulated juices to the skillet. Spoon sauce generously over steaks and heat through for 1 minute. Sprinkle with fresh chopped parsley and serve immediately.