Preheat oven to 400 degrees. Place butter in a cast-iron skillet and place in the oven while it heats up. Keep a watch on the butter. Once it has melted, remove the skillet and allow the oven to finish heating. Carefully swirl the butter around in the skillet to coat the bottom and sides.
In a medium-sized bowl, place the cornmeal, flour, sugar, baking soda, and salt and stir to combine.
Add the milk and eggs to the cornmeal mixture. Slowly whisk in the melted butter.
Stir until the batter is completely mixed, being careful not to over mix.
Pour the batter into the cast iron skillet. Bake for 20 – 22 minutes or until golden brown and a toothpick inserted in the center comes out clean.
Remove from the oven and carefully invert the skillet onto a plate. Prop the bottom of the cornbread slightly with a spoon or fork to allow steam to escape.