Preheat the oven to 400° F. Place a 12-inch cast-iron skillet into the oven to preheat.
Whisk together the cornmeal, all-purpose flour, sugar, baking powder, salt, and baking soda in a large bowl.
Whisk together the creamed corn, eggs, buttermilk, and oil in a medium bowl.
Add the butter to the skillet in the oven and let it melt. Watch it carefully, it only takes about 2 minutes.
Add the wet ingredients to the dry ingredients, and stir just to combine.
Use potholders to remove the skillet from the oven. Use a spoon to swirl the butter around the skillet. Carefully pour the batter into the hot skillet and carefully stir it a bit to incorporate the melted butter into the batter. It doesn’t have to be fully incorporated.
Bake until the cornbread is puffed, golden along the outside, and a toothpick inserted in the center comes out with just a couple crumbs, about 28 minutes.