1. Whisk together egg and buttermilk. Combine cornmeal mix, salt, pepper, and 1/4 cup flour in a shallow dish. Dredge tomato slices in remaining 1/4 cup flour; dip in egg mixture, and dredge in cornmeal mixture.
2. Pour oil to a depth of 1/2 inch in a large cast-iron skillet; heat to 375° over medium-high heat. Drop tomatoes, in batches, into hot oil, and cook 2 minutes on each side or until golden. Drain on paper towels. Sprinkle hot tomatoes with salt to taste.