In a sealed plastic bag and using the flat side of a meat mallet or a rolling pin, coarsely crush peppercorns. Press crushed peppercorns onto both sides of steaks. Evenly sprinkle with salt.
Heat a 10-inch cast-iron skillet over medium-high heat until hot. Add oil, swirling to coat bottom of pan. Add steaks to skillet, cooking until browned on each side and to desired degree of doneness, about 5 minutes per side for medium-rare.
Transfer steaks to a plate, and tent with foil to keep warm.
Reduce heat to medium-low. Add shallot to skillet, scraping up any brown bits with a wooden spoon. Cook until tender, about 3 minutes.
Add cognac and heavy cream to skillet. Cook, until slightly reduced, approximately 1 minute. Add butter, stirring constantly, until mixture is thickened. Remove from heat, and stir in vinegar.
Serve sauce immediately with steaks.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/steak-au-poivre-recipe/