Wrap peppercorns in a clean dishtowel, then crush, either by pressing firmly with the bottom of a heavy skillet or by tapping with a mallet.
Transfer pepper to a plate, then roll steaks in it so that they are evenly coated.
Season liberally both sides with salt.
Heat butter and oil in a large skillet over medium-high heat.
Add steaks and cook until well browned, about 4 minutes on each side for medium-rare.
Transfer steaks to a warm plate. Cover loosely with foil to keep warm.
Add cognac to the hot pan, then carefully ignite with a long-handled match. (Keep a lid handy so the flame can be extinguished). Allow the alcohol to burn off, about 1 minute, then add the stock.
Cook until reduced by half, about 4 minutes.
Add cream and cook, stirring occasionally until thick, 3-5 minutes.
Season with salt and pepper and pour over plated steaks.