Preheat the oven to 400 degrees. Add a tablespoon of unsalted butter to a cast iron skillet and heat it in the oven for about 5 minutes, until the butter is melted.
Whisk all of the dry ingredients in a medium bowl. Add in the cooled, melted butter, then the eggs and buttermilk. Whisk until smooth.
Remove the skillet from the oven and carefully pour the batter in. Bake for 30 minutes or so, or until the cornbread is cooked through and golden brown.