Preheat the oven to 375 degrees F. Butter an 8-inch square baking pan and set aside.
Combine the cornmeal, flour, sugar, kosher salt, baking powder and baking soda in a large bowl and set aside. Whisk together the butter, buttermilk and eggs in a bowl and stir to combine. Pour the buttermilk mixture into the cornmeal mixture and stir until smooth, then fold in the Cheddar cubes, grated Parmesan and ½ cup shredded Cheddar.
Pour the batter into the prepared pan and bake for 25 minutes. Sprinkle the remaining ½ cup Cheddar on top of the batter and continue to bake until the cheese is bubbling, the cornbread bounces back when pressed with a finger and a cake tester comes out clean, 10 minutes more.
