Place the fish on a cutting board and pat dry with a paper towel.
In a medium shallow pan, combine 1 cup flour, cornmeal, cornstarch, baking powder, garlic powder, mustard, smoked paprika and Original Seasoning, or salt and pepper.
In small, shallow pan, whisk together the remaining 4 tablespoons of flour and soda. Adjust the ingredients until you achieve a consistency thinner than pancake batter.
Dip the fish in the wet mixture, then dredge through the flour mixture to coat generously. Lightly shake any excess coating off and place on a wire rack. For a thicker crust, dip the fish back in the wet mixture and dredge through flour again. Let the fish rest on the wire rack for 5 minutes before frying.
Meanwhile, add about 3 inches of oil to a saucepan, Dutch oven or deep fryer and heat to 350 degrees F.
Place a few fish in the oil at a time. Cook for about 4 minutes, flipping fish occasionally, or until they are a rich golden brown. Place on a wire rack. Let cool slightly and serve with tartar sauce.