In a spice grinder, pulverize the porcini to a fine powder; transfer to a small bowl. Add 1 tablespoon of the porcini powder to 1½ cups water; set aside. In the spice grinder, pulse the peppercorns until coarsely ground. Stir the pepper and 1½ teaspoons salt into the remaining porcini powder; sprinkle and rub over the steaks. Add any seasoning that falls off to the porcini water.

In a 12-inch skillet over medium-high, heat the oil until barely smoking. Add the steaks, reduce to medium and cook until the centers reach 120°F for medium-rare, 10 to 12 minutes; flip halfway through. Transfer to a platter. Discard any fat in the pan.

In the same pan over medium, melt the butter. Add the shallot and cook, stirring, until softened, about 2 minutes. Off heat, add 3 tablespoons of the brandy. Return to medium and cook, scraping up the browned bits, until slightly reduced. Add the porcini water; cook over medium-high, stirring, until a spatula drawn through leaves a trail, 8 to 10 minutes. Whisk in the crème fraîche, remaining 1 tablespoon brandy and any steak juices; cook, whisking, until slightly thickened, 2 to 3 minutes. Off heat, taste and season with salt and pepper. Slice the steaks, return to the platter and pour the sauce over them. Sprinkle with chives.