Whisk together the egg and the buttermilk.In a shallow dish combine the cornmeal, baking powder, salt, pepper and ¼ cup of the gluten free flour. Dredge the tomato slices in the remaining ½ cup of gluten free flour; dip in the egg mixture, and dredge in the cornmeal mixture.Pour the oil to a depth of ½ inch in a large cast iron skillet. Heat the oil to 350°F over medium-high heat. Drop the tomatoes, in batches, into hot oil and cook for 2 minutes or until golden. Drain on paper towels. Sprinkle hot tomatoes with sea salt to taste.