Step 1: Prepare the Tomatoes. Wash the green tomatoes and slice them into 1/4-inch thick rounds. Discard the ends. Lay the slices on a layer of paper towels and sprinkle lightly with salt and pepper. Let them sit for about 10-15 minutes; this draws out some moisture and enhances their flavor. Pat them dry with fresh paper towels before breading.
Step 2: Set Up Breading Stations. In a shallow bowl or plate, combine the flour, 1/2 teaspoon salt, 1/4 teaspoon black pepper, baking powder (if using), and garlic powder. Mix well. In a second shallow bowl, whisk together the buttermilk and egg until well combined. If your buttermilk is very thick, you can thin it slightly with 1/4 cup of regular milk. In a third shallow bowl, add the cornmeal.
Step 3: Bread the Tomatoes. Working one tomato slice at a time, first dredge it lightly in the flour mixture, shaking off any excess. Then dip it into the buttermilk-egg mixture, ensuring it's fully coated. Finally, press it firmly into the cornmeal, making sure both sides are well-covered. Place the breaded slices on a clean plate or baking sheet. Do not stack them.
Step 4: Heat the Oil. Pour 1-2 cups of vegetable oil into a large, heavy-bottomed skillet (cast iron works wonderfully) to a depth of about 1/2 to 3/4 inch. Heat the oil over medium-high heat until it reaches about 350-375°F (175-190°C). If you don't have a thermometer, a small pinch of cornmeal should sizzle vigorously when dropped in.
Step 5: Fry the Tomatoes. Carefully place a few breaded tomato slices into the hot oil, ensuring not to overcrowd the skillet. Fry for 2-3 minutes per side, or until golden brown and crispy. The exact time will depend on your oil temperature and the thickness of your slices.
Step 6: Drain and Serve. Once golden and crispy, remove the fried green tomatoes with a slotted spoon or tongs and place them on a wire rack set over paper towels to drain excess oil. Immediately sprinkle with a little extra salt while they are hot. Serve immediately with your favorite dipping sauce. For best results, avoid letting them sit for too long, as they lose their crispness.