Allow the fish to come to room temperature for about 30 minutes. Pat dry and season on both sides with salt and pepper, to taste.
In a shallow dish, whisk together flour, cornmeal and baking powder. In a separate shallow dish, whisk together the egg and buttermilk.
Pour the oil to a depth of 2 ½ inches in a Dutch oven or other heavy-bottomed pot. Heat the oil over medium-high heat to a temperature of about 375 degrees F.
Dip each piece of fish in the egg mixture first, gently shaking off the excess, and then into the flour mixture to coat. Shake off any extra coating. Place the battered fish on a wire rack.
Working in batches, if necessary, carefully place the fish in the hot oil. Cook until golden brown, about 4 minutes. Gently turn and cook until golden on the other side, about 3 more minutes. Remove from the oil and drain on a paper-towel lined tray. Lightly salt the fillets as soon as they come out of the oil.
Place the first batch of fish in a 200 degree F oven to keep warm while you cook the second batch.
Serve on buttered, toasted rolls with lettuce, tomato and tartar sauce.