An hour before you want to make this recipe, remove the steaks from the refrigerator and let them come to room temperature.
Meanwhile, prepare all the ingredients for the sauce next to your stovetop: measure out the Cognac in a small ramekin, grind the pepper into a small bowl (measuring as you go), measure out the crème fraiche and the salt. Place a large lid next to your saucepan.
In a large sautoir or saucepan, melt the butter over medium heat until it’s foaming. Add the oil and swirl the fats around the pan, then increase the heat to medium-high.
Cook the steaks to your desired doneness. (Ask your butcher how long to cook for each side for your taste, because this step will necessarily depend on the thickness of your steaks.)
Removing the saucepan momentarily from the heat, place the steaks on a platter and sprinkle a pinch of salt over each steak. Cover the platter very loosely with a sheet of aluminum foil.
Now make the pan sauce: place the saucepan back onto medium heat and add the Cognac. There is no need to do a parlor-trick flambé, but if the Cognac does flare up, just cover with a lid to douse the flames.
Add the ground pepper and swirl, using a flat spatula to scrape up the browned bits stuck to the bottom of the pan.
Lower the heat a bit. Reduce the Cognac until it’s syrupy and there’s only about a tablespoon left in the pan. Add the crème fraiche and continue reducing and stirring to homogenize the pan sauce. Check the steaks on the platter: there should be meat juices surrounding them. Pour those meat juices into the sauce reducing on the stove.
Finally, when you have about 1 cup of sauce left in the pan, add the salt and stir well. Serve the steaks for 4-5 diners or warmed plates, taste your sauce (it may need more salt), and serve the sauce over the steaks. Bon app’!