The fillets should be at room temperature. Heat a large cast-iron skillet over very high heat until it is beyond the smoking stage and you see white ash in the skillet bottom, at least for 10 minutes. Meanwhile, pour 2 tablespoons melted butter in each of 6 small ramekins; set aside and keep warm. Reserve the remaining butter. Heat the serving plates in a 250-degree oven. Dip each fillet in the reserved melted butter so that both sides are well coated. Then, mix thoroughly all the spices for blackening mixture and sprinkle the Blackening Spice Mixture generously and evenly on both sides of the fillets. Place 1 or 2 fillets in skillet and cook uncovered over very high heat until the underside becomes deep brown, almost black (but not burned), about 2 minutes (the time may vary according to the fillet's thickness and the heat of the skillet). Turn the fish over and pour 1 teaspoon of butter on top of each. Cook until fish is done, about 2 minutes more. Repeat with remaining fillets. Serve each fillet while hot. To serve, place 1 fillet and a ramekin of butter on each plate.
Recipe Courtesy of George Hirsch, author, "Know Your Fire"