1 Brush salmon fillets on both sides with 1/4 cup butter, and sprinkle evenly with the cayenne pepper mixture. 2  Drizzle one side of each fillet with 1/2 remaining butter. 3  In a large, heavy skillet over high heat, cook salmon, butter side down, until blackened, 2 to 5 minutes. In a large, heavy skillet over high heat, cook salmon, butter side down, until blackened, 2 to 5 minutes. 2  Turn fillets, drizzle with remaining butter, and continue cooking until blackened and fish is easily flaked with a fork.