A hot, crunchy peppercorn crust makes steak au poivre one of the best beef dishes ever created. Here, a blend of heat, aroma, and fruitiness is formed by three kinds of peppercorns: green,classic black, and Szechuan, with its woodsy tang.
Preheat oven to 400 degrees. Crush peppercorns and coriander with a mortar and pestle, or with the bottom of a heavy skillet. Spread onto a large dish or a baking sheet.
Season steaks with salt, and coat both sides with ground peppercorn mixture by patting into flesh. Heat oil in an ovenproof skillet (preferably cast-iron) over medium-high heat. Sear steaks until golden brown, about 2 minutes per side. Transfer skillet to oven, and cook steaks about 6 minutes, for medium-rare.
Remove steaks from skillet, and let rest for 10 minutes, reserving juices. Meanwhile, wipe out skillet. Add vinegar, and cook until reduced by half, about 5 minutes. Swirl in reserved steak juices, and the butter. Slice steaks, and serve with sauce.