Combine egg and buttermilk; set aside.
Combine 1/4 cup all-purpose flour, cornmeal, 1 teaspoon salt, and pepper in a shallow bowl or pan.
Dredge tomato slices in remaining 1/4 cup flour; dip in egg mixture, and dredge in cornmeal mixture.
Pour oil to a depth of 1/4 to 1/2 inch in a large cast-iron skillet; heat to 375°. Drop tomatoes, in batches, into hot oil, and cook 2 minutes on each side or until golden. Drain on paper towels or a rack. Sprinkle hot tomatoes with salt.