1. Preheat oven to 425°. Whisk together first 5 ingredients in a large bowl. Whisk together buttermilk and eggs; stir into cornmeal mixture just until combined. Heat a 10-inch cast-iron skillet over medium-high heat until it just begins to smoke. Add butter, and stir until butter is melted. Stir melted butter into cornbread batter. Pour batter into hot skillet.
2. Bake at 425° for 25 to 30 minutes or until golden and cornbread pulls away from sides of skillet. Invert cornbread onto a wire rack; serve warm.