Place cast iron skillet in the middle rack of oven and preheat to 400°F.
Combine flour, cornmeal, baking powder, and salt in a small mixing bowl and set aside.
In a large mixing bowl, whisk together the eggs, buttermilk, and maple syrup. While continuing to whisk, slowly pour in the 4 tablespoons of melted butter.
Pour the dry ingredients into wet and mix about 6-8 times until it just begins to come together.
Add the sweet potato and fold the batter another 12-15 times until the batter is just combined.
Using oven mitts, remove the skillet from the oven and swirl 1 tablespoon of butter to coat the pan.
Pour the batter into the skillet and spread out into an even layer using a spatula.
Bake for 25 minutes, until golden brown and a knife inserted in the center comes out clean.
Brush the top with remaining butter, allow to cool for 10 minutes, and serve.