01 - Pat steaks thoroughly dry with paper towels, then season both sides generously with kosher salt and freshly ground black pepper.
02 - Heat olive oil and 1 tablespoon butter in a large skillet over medium-high heat until butter foams. Add steaks and sear for 2 to 3 minutes per side for medium-rare doneness, adjusting time for desired results. Transfer steaks to a plate and tent loosely with aluminum foil to rest.
03 - Reduce heat to medium. Add remaining 2 tablespoons butter to the skillet. Add sliced mushrooms and sauté for 3 to 4 minutes until softened and lightly browned.
04 - Stir in diced shallots and minced garlic; cook for 1 minute until fragrant, being careful not to burn the garlic.
05 - Stir in Dijon mustard, then carefully pour in brandy. Let simmer for 1 to 2 minutes to reduce slightly and cook off the alcohol, stirring to release any browned bits from the pan bottom.
06 - Pour in beef broth, Worcestershire sauce, and heavy cream. Simmer for 3 to 5 minutes, stirring occasionally, until sauce thickens enough to coat the back of a spoon.
07 - Return steaks and any accumulated juices to the skillet, spooning sauce over the meat. Cook for 1 to 2 minutes just to heat through. Sprinkle with fresh parsley and serve immediately with additional sauce on the side.