Soak tomato slices: Place tomato slices and buttermilk in a medium bowl; set aside. Combine flour, cornmeal, salt, and pepper in a small brown paper bag; set aside.
Heat frying oil: Add vegetable oil or drippings to a large cast-iron skillet or other heavy skillet to a depth of ½ inch. Heat over medium-high until the oil shimmers.
Add breading to tomatoes: Meanwhile, remove 3 or 4 tomato slices from buttermilk, letting excess drip off; add to flour mixture in paper bag. Close bag, and shake gently until tomato slices are well coated.
Fry tomato slices: Place coated tomato slices in hot oil. Fry until golden brown on both sides, turning often to avoid sticking, about 4 minutes. Drain on paper towels.
Repeat in batches: Repeat coating-and-frying process with remaining tomato slices. Serve hot with bacon or sausage.
