Place a 10-inch cast iron skillet in the oven and preheat to 400°F. Let the skillet heat for a full 20 minutes.

In a large bowl, whisk together the cornmeal, flour, baking powder, baking soda, and salt. Make a well in the center.

In a separate bowl, whisk together the melted butter, buttermilk, eggs, and 2 tablespoons of the oil or bacon fat.

Pour the wet ingredients into the dry ingredients and fold with a spatula until just combined. The batter will be lumpy — do not overmix.

Carefully remove the hot skillet from the oven. Swirl the remaining 1 tablespoon of oil or bacon fat around the bottom and sides of the skillet. Pour in the batter and spread evenly.

Return the skillet to the oven and bake for 16 to 23 minutes until golden on top and a toothpick inserted in the center comes out clean. Cool on a wire rack for 15 minutes, then cut into wedges and serve warm.