Slice the tomatoes and place in a single layer on a baking sheet covered with several layers of paper towels. Sprinkle with ½ teaspoon coarse salt. Set aside for 30-minutes.
Preheat oven to 400°F. Grease an 8 or 9-inch cast iron skillet. Place the skillet in the oven to preheat.
In a large mixing bowl whisk together the flour, cornmeal, sugar, baking powder and ½ teaspoon table salt.
In a separate small bowl whisk the egg until blended. Add the buttermilk, mayonnaise and vegetable oil and whisk until combined.
Pour the buttermilk mixture into the flour and add the corn, basil and ½ cup of the grated Parmesan cheese. Gently fold everything together until blended. Don’t overmix.
Remove the preheated skillet from the oven. Carefully pour the batter into the hot skillet.
Pat the tomato slices dry and arrange on top of the batter. Sprinkle with the remaining Parmesan cheese. Bake for 25 to 30 minutes or until a toothpick comes out clean when inserted into the center.
OPTIONAL: Prop the oven door open and turn the oven to high-broil. Bake the cornbread under the broiler until the top is golden brown, the tomatoes are bubbling and the cheese is melted. Watch it carefully as this only takes a minute.
Remove from the oven and cool 15 minutes. Garnish with additional basil and slice into wedges. Serve with butter or goat cheese.