In the same saute pan that has not been cleaned out, dump all but 1 Tbsp of fat. Carefully add the cognac to the hot pan to deglaze the pan. Over low heat stir to scrape the bits off bottom of pan. Increase to medium heat and add the beef stock, cream and peppercorns. Bring to a boil then turn down to simmer, allowing the sauce to reduce and thicken, 3-4 minutes. If at this point you prefer a thicker sauce, you can add a thickening agent (such as cornstarch and water mixture (slurry)) just be sure to bring it to a boil again to activate the thickener fully. Once desired thickness of the sauce is achieved, remove from heat and taste for salt. Off heat whisk in the cold butter until sauce is glossy and butter is melted. Serve immediately on top of the steaks.