Prepare the steaks: Remove the steaks from the refrigerator about 20–30 minutes before cooking so they can come to room temperature. Pat them completely dry with paper towels to ensure a proper, golden sear. Crush the whole black peppercorns using a mortar and pestle or place them in a zip bag and gently crush them with a rolling pin. The texture should be coarse, not powdery. Press the crushed pepper firmly onto both sides of each steak so it adheres well. Lightly season with salt.

Sear the steaks: Heat olive oil in a heavy skillet (preferably cast iron) over medium-high heat until hot but not smoking. Carefully place the steaks into the pan without overcrowding so they sear instead of steam. Cook for about 3–4 minutes per side for medium-rare, adjusting the time depending on thickness and desired doneness. During the last minute of cooking, add butter and smashed garlic to the pan. Tilt the skillet slightly and continuously spoon the melted butter over the steaks to enhance flavor and create a rich crust. Remove the steaks and let them rest on a plate loosely covered with foil for at least 5–10 minutes to allow the juices to redistribute.

Make the sauce: Lower the heat slightly. Carefully pour the brandy or cognac into the hot skillet (be cautious as it may briefly flame). Let it simmer for about 1–2 minutes, scraping up all the flavorful browned bits from the bottom of the pan. Add the beef broth and allow it to reduce by half, intensifying the flavor. Stir in the heavy cream and Dijon mustard if using. Simmer gently for 3–5 minutes until the sauce thickens and becomes smooth, creamy, and glossy. Taste and adjust seasoning if needed.

Serve: Either return the rested steaks to the pan briefly to coat them in the sauce, or place them on serving plates and spoon the creamy pepper sauce generously over the top. Garnish with freshly chopped parsley for color and freshness. Serve immediately while hot for the best texture and flavor.