Preheat a large cast iron or stainless steel skillet over medium heat. Thoroughly dry the steaks with paper towels, season with kosher salt, then press both sides firmly into the crushed black peppercorns to create an even crust. Pour the neutral oil into the heated pan; when it shimmers, lay the steaks in and sear undisturbed for about 4 minutes per side. If excess fat lines the steak edges, hold the steaks upright with tongs to sear the sides until deeply browned. Cook to your desired doneness—aim for an initial internal temperature of 120–125°F for a medium-rare finish of 130–135°F. Transfer steaks to a cutting board, tent with foil, and allow them to rest. Carefully discard excess fat from the pan, then add the minced shallot with a pinch of salt and sauté for 2–3 minutes until softened. Remove the pan from the burner to pour in the cognac, then return to medium-high heat, cooking until the liquid nearly evaporates, about 2 minutes. Stir in the heavy cream, bring to a gentle simmer, and cook until the sauce thickens enough to coat the back of a spoon, around 2–3 minutes. Incorporate the optional green peppercorns, season with additional salt as needed, then remove from heat and whisk in the cold butter until smooth. Spoon a portion of the sauce onto each plate, arrange the steaks over the sauce, and generously drizzle the remaining sauce over the top. Serve immediately.