Warm a large stainless steel or cast iron skillet over medium heat. The pan is ready when it feels evenly hot across the cooking surface and the oil will shimmer rather than sit still.

Blot the steaks thoroughly with paper towels, then season them with kosher salt and press both sides into the crushed black peppercorns. Press firmly enough for the pepper to adhere, leaving a rugged crust with visible pieces rather than a dusty coating.

Pour the neutral oil into the hot skillet and add the steaks when the oil shimmers, leaving space between them. Sear without moving them for 4 minutes per side, then brown any thick side fat by holding the steaks upright with tongs. The crust should turn deep brown and smell toasty, while the fat edge becomes golden and rendered.

Check the steaks for your preferred doneness, then transfer them to a cutting board and tent loosely with foil for 5 minutes. For medium-rare, remove the steaks at 120 to 125°F so carryover heat can bring them to 130 to 135°F as they rest.

Carefully pour off excess pan fat, then cook the minced shallot with a pinch of salt for 2 to 3 minutes. Remove the skillet from the heat before adding the Cognac or brandy, then return it to medium-high heat and reduce for about 2 minutes. The shallot should be soft and fragrant, and the Cognac should reduce until only a small amount remains in the pan.

Add the heavy cream and bring it to a gentle simmer for 2 to 3 minutes. Stir and scrape up the browned bits as the sauce thickens enough to coat the back of a spoon cleanly.

Stir in the green peppercorns, if using, and season the sauce with salt to taste. Turn off the heat, whisk in the cold butter, then divide one-quarter of the sauce between two plates before adding the steaks and spooning over the rest. The finished sauce should look glossy and flow slowly around the steak rather than appear oily or thin.