01 - Pat steaks thoroughly dry with paper towels. Season both sides generously with kosher salt and freshly ground black pepper, pressing seasoning into the meat.
02 - Heat olive oil and 1 tablespoon butter in a large skillet over medium-high heat until butter foams. Add steaks and sear for 2-3 minutes per side for medium-rare, or until desired doneness is achieved. Remove steaks to a plate and tent loosely with aluminum foil.
03 - Reduce heat to medium. Add remaining 2 tablespoons butter to the skillet. Add sliced mushrooms and sauté for 3-4 minutes, stirring occasionally, until mushrooms release moisture and begin to brown.
04 - Add diced shallots and minced garlic to the mushrooms. Cook for 1 minute, stirring constantly, until fragrant and shallots become translucent.
05 - Stir in Dijon mustard until well combined. Carefully pour in brandy or cognac. Let mixture simmer for 1-2 minutes, stirring occasionally, until slightly reduced and alcohol aroma dissipates.
06 - Pour in beef broth, Worcestershire sauce, and heavy cream. Simmer for 3-5 minutes, stirring occasionally, until sauce thickens enough to coat the back of a spoon.
07 - Return steaks and accumulated juices to the skillet. Spoon sauce generously over steaks. Cook for 1-2 minutes to heat through. Garnish with fresh parsley and serve immediately with extra sauce on the side.