Thaw fish, if frozen. Rinse; pat dry with paper towels. In a shallow dish combine egg and buttermilk. In another shallow dish combine cornmeal, flour, salt, and pepper. Dip fish into egg mixture. Then roll fish in cornmeal mixture.
In a 12-inch skillet cook bacon over medium-low heat for 6 to 8 minutes or until crisp, turning often. Drain on paper towels; crumble into large pieces. Set aside.
Using the same skillet, remove all but 2 tablespoons of the drippings; reserve remaining drippings. Heat over medium heat. Add onions. Fry for 5 to 7 minutes or until tender but not brown, stirring often. Transfer to a 13 x 9 x 2-inch baking pan; keep warm in a 300 degree F oven.
In the same skillet heat 3 tablespoons of the reserved drippings over medium heat, adding shortening or oil, if needed. Add 2 of the fish. Fry for 5 to 7 minutes or until golden. Turn carefully. Fry for 5 to 7 minutes more or until golden and crisp and fish flakes easily with a fork.
Drain on paper towels. Place in the same pan with onions; return to the oven. Repeat frying remaining fish, addition additional shortening or oil as needed. To serve, arrange fish on a platter; spoon onions over fish. Sprinkle with bacon. Serve with Tartar Sauce recipe or purchased tartar sauce, if desired. Makes 4 servings.