01 - Pat steaks thoroughly dry with paper towels. Season both sides generously with salt and freshly ground black pepper.
02 - Heat olive oil and butter in a large skillet over medium-high heat until butter foams. Add steaks and sear for 2-3 minutes per side for medium-rare doneness, adjusting time as needed for preferred doneness. Transfer to a plate and tent loosely with foil to rest.
03 - In the same skillet, add sliced mushrooms and sauté for 3-4 minutes until golden brown. Add minced shallots and garlic; cook for 1 minute until fragrant, being careful not to burn the garlic.
04 - Carefully pour brandy or cognac into the skillet. If desired and safe, ignite with a long lighter to flambé and burn off alcohol. Let the liquid reduce by half for 1-2 minutes.
05 - Stir in heavy cream, Dijon mustard, Worcestershire sauce, and fresh lemon juice. Simmer for 2-3 minutes, stirring occasionally, until sauce thickens and coats the back of a spoon.
06 - Return steaks and any accumulated juices to the skillet. Spoon sauce over steaks and simmer for 1 minute to rewarm through. Sprinkle with chopped fresh parsley and serve immediately.