Adjust oven rack to middle position; heat oven to 400 degrees. Spray 8-inch square baking dish (glass is recommended) with nonstick cooking spray.
Whisk flour, cornmeal, baking powder, salt, and baking soda in medium bowl until combined; set aside.
In food processor or blender, process sugar, thawed corn kernels, and buttermilk until combined, about 5 seconds.
Add eggs and process until well combined (corn lumps will remain), about 5 seconds longer.
Using rubber spatula, make well in center of dry ingredients; pour wet ingredients into well. Begin folding dry ingredients into wet, giving mixture only a few turns to barely combine; add melted butter and continue folding until dry ingredients are just moistened.
Pour batter into prepared baking dish; smooth surface with rubber spatula. Bake until deep golden brown and toothpick inserted in center comes out clean, 25 to 35 minutes. Cool on wire rack 10 minutes; invert cornbread onto wire rack, then turn right side up and continue to cool until warm, about 10 minutes longer. Cut into pieces and serve.