Prepare the Steaks
Season the steaks with salt on both sides. Press the crushed black peppercorns onto both sides of the steaks, coating them evenly for a flavorful crust. Set aside to rest while you heat the skillet.
Sear the Steaks
In a large skillet, heat the butter and olive oil over medium-high heat until hot but not smoking. Carefully add the steaks and cook for 3-4 minutes on each side for medium-rare, or adjust based on your desired doneness. Once done, transfer the steaks to a plate and cover with foil to keep warm.
Make the Pan Sauce
Carefully add the cognac to the skillet, using caution as it may briefly flame. Stir and scrape up any browned bits from the pan. Let the cognac reduce by half, about 1-2 minutes.
Add Cream and Mustard
Lower the heat to medium, then add the heavy cream and Dijon mustard (if using). Stir to combine and simmer until the sauce thickens, about 3-5 minutes. Taste and adjust seasoning with salt if needed.
Serve
Pour the creamy pepper sauce over the steaks and garnish with fresh parsley.